Mathematics Education Project Shaun Mooney April 5, 2013 1 Contents 1 Teaching Experience 1.1 Alexandra College . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Trinity College Dublin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4 4 2 Topic 6 3 History of Differentiation 3.1 Newton-Leibniz Controversy . . 3.2 Early Work . . . . . . . . . . . 3.3 16th Century . . . . . . . . . . 3.4 Newton & Leibniz . . . . . . . . 3.5 Controversy Over Infinitesimals 3.6 Cauchy & Weierstrass . . . . . . . . . . . 7 7 7 9 9 10 11 4 Differential Calculus in the Curriculum 4.1 History of Differential Calculus in the Leaving Certificate . . . . . . . . . . . 12 12 5 Teaching Plan 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Lesson Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 14 14 15 References 34 . . . . . . . . . . . . . . . . . . 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgments I would like to thank Elizabeth Oldham for putting on a such an interesting course and also for being so patient and understanding. I learnt a lot of things in this class that I believe will serve me well in the years to come. I must also think Professor Donal O’Donovan for organising the schools for us and Emma Howard for all of her help over the course of this project. 3 Part 1 1 1.1 Teaching Experience Alexandra College For part of my teaching experience I spent one class in Alexandra College. The class was a third year one and the students were borderline pass according to the teacher. They were in the process of learning about the volume of three dimensional shapes, mostly cylinders, and it was a purely behaviourist class with little cognitive or constructivist learning. The whole class was taken up with correcting homework which most of the students had not seemed to have done. Unfortunately I did not have an opportunity to witness any part of the project maths course due to the short amount of time that I spent there. I was treated to a class of behaviourist learning. The students were attempting exam style questions and they clearly did not understand what they were doing. Most of them had to turn back pages in order to try and link aspects of certain questions together and apparently try and “force” the question to work out (at least that is what I gathered from my perspective. Of course, this is my own opinion from what I observed and I may be, and hope I am, completely wrong. However, the way that the students approached the class leads me to believe that I am right. There were many feeble excuses for why the homework was not done, all of which I have heard from my own schooling days). I must say that I was very impressed with the teacher in the way that she handled the class. I felt that she was rather handicapped by the nature of the class, but I feel that that was not her fault. The maths syllabus, and the Irish education system in general, does not lend itself to the type of learning that is required to properly develop the minds of the young generation. There seemed to be far too much teaching to the exam rather than any actual learning of maths. As I say, this is a shortcoming of the system rather than the teacher. I can not help but feel that they are as much victims of this system as the students. As I have already stated, I was only present for one class. It may be that I happened to be present for the one and only such class. However, I fear that this is not the case. 1.2 Trinity College Dublin As well as the above teaching experience I also spent some time helping mature BESS students in Trinity College Dublin. The major problem with BESS students is that many of them are more interested in their other subjects and do not like maths. As the maths and statistics is based on economics, there is a lot of calculus and probability on the course. I was mainly helping with the maths side of things. There seemed to be a severe lack of understanding of fundamental concepts in maths. The most worrying of these was that they struggled with the ideas of what functions are and how to deal with them 4 properly. When dealing with differentiation some people had trouble understanding that y is a function of x and, while I attempted to convince them, I’m not sure that they understood it properly. I also had to explain how to differentiate a function as well as using the product rule, quotient rule and chain rule. While these issues are quite alarming, they are also predictable. Since it is a mix of multiple different subjects, BESS is a subject that attracts many different types of people and that means that there will be quite a high proportion of people who do not like maths. 5 Part 2 2 Topic The topic I have chosen to look at for this project is differentiation. I chose this topic for many reasons. Firstly, it has always been an area that I am very interested in. Ever since my secondary school teacher first went through the mechanics of calculus I have found it very interesting. I am also extremely interested in the research options related to calculus. For my final year project I looked at interactions of partial differential equations which are completely based on calculus. The idea of calculus is, in my opinion, one of the greatest formulated in modern maths. It is not a coincidence that it is used in nearly all areas of maths. It is the cornerstone of whole areas of the subject and yet nobody still really knows who first discovered it. 6 3 3.1 History of Differentiation Newton-Leibniz Controversy Depending on who you were to ask you would get different answers on who discovered calculus. In this area of the world Isaac Newton would be considered to be the first person to have formulated calculus. However, a German, say, might disagree and claim it was in fact Gottfried Leibniz who must take the lion’s share of the credit. This controversy has come to be known, rather unimaginatively I might add, as the Newton-Leibniz Controversy. Nowadays, since science is not as competitive as once it was, credit is generally given equally to both men. Back in the day, however, there was great debate over which man deserved greater recognition. 3.2 Early Work When Newton and Leibniz formulated their respective theories they did not think about limits as we do today; they worked with infinitesimals. Infinitesimals are quantities that are infinitely small. They are as close to zero as it is possible to get without actually being zero. To see an example of infinitesimal numbers, consider the graph f (x) = x1 . It can been seen from the graph that, as x → ∞, f (x) → 0. However, f (x) will never be 0. The curve makes an asymptote with f (x) = 0, i.e. it will never touch the line. This idea had been in circulation in the maths world well before the late 1600’s. Infinitesimals and the idea of infinity can be traced back to Ancient Greece and the mathematicians and philosophers of antiquity. Zeno of Elea(490BC-430BC) famously posed paradoxes, many pf which are about the infinite[17]. One of the most famous of these is ’Achilles and the Tortoise’ which states that, in a race, if the slowest runner (the tortoise) will never be over-taken by the faster runner (Achilles). We allow the slow runner to be slightly ahead with a speed much less than the fast runner. However, in every moment of time the slower runner moves a non-zero distance. Therefore, in each of these moments the fast runner must first reach where the slow runner was in the previous moment. This problem looks at time a discrete, disjoint quantity and to anybody today the flaws are obvious. Another famous and similar problem is that of ’The Arrow’, which says that an arrow will never reach it’s target and, hence, that movement is infinite. Again, Zeno splits time into moments and claims that in order to traverse the full distance, the arrow must first fly half the distance, then half that again, etc. Therefore, it will never reach it’s target; the distance just keep being halved. These problems perplexed most Greeks, as was noted by Aristotle: “Zeno’s arguments of motion, which cause so much disquietude to those who try to solve the problems”[8]. 7 However, Aristotle, himself, dismissed the paradoxes, saying that reducing time to moments “is not granted”[8]. There were many reasons why the Ancient Greeks found Zeno’s ideas hard to comprehend, not least of which being their number system. They were not as fortunate as we are today with our decimal number system[18]. This meant that they could only really work in whole √ numbers, or, to be more precise, finite whole numbers. This is why the proof that 2 is irrational caused such furore. This inability to deal with infinity lead to something called the method of exhaustion which was effectively an early form of calculus[4]. The person most famous for implementing the method of exhaustion is Archimedes of Syracuse (287BC-212BC) in his book entitled “The Method of Mechanical Theorems” or, more simply, “The Method”. The aforementioned method is a pre-calculus way of computing areas. We do this today with integration which uses limits, but before there were limits, the Greeks would define area by saying that the area of one object is similar to the area of another. For example to get the area of a circle of radius r it could be compared to a triangle whose height is the same as the radius of the circle and whose base is the same as the circumference of the circle[5]. So, 1 (r) (2πr) 2 = πr2 Area of triangle = (1) = Area of circle Archimedes’ use of the method of exhaustion to find the area of a circle was to construct a circumscribed and inscribed n-sided polygon (see figure 1) and to estimate the area this way. Figure 1: Archimedes’ method of exhaustion for finding the area of a circle[6] 8 The Greeks also had no concrete definition of length. In fact, today we define length in terms of limits and, so, Archimedes and his peers had to limit themselves to relatively simple curves. However, they were not limited to two dimensions. We also know that they could find the volume of shapes such as cones, cylinders and spheres[11]. 3.3 16th Century For over a thousand years the development of calculus remained relatively static. In the 16th century Johannes Kepler(1571-1630), on realising that the orbit of the planets could not be circular but elliptical, cut an ellipse into segments and summed them to find the area of it. Similarly, Bonaventura Cavalieri (1598-1647) and Pierre de Fermat(1602-1665), among many others, used this method of indivisibles in order to sum the area under curves and surfaces[10]. For example, Cavalieri showed that Z a xn = 0 an+1 n+1 (2) and Fermat showed that the derivative at the maxima and minima (or turning points) are zero. These were clearly early attempts at integration[6]. These mathematicians managed to, unknowingly, evaluate many integrals and set up the basis for integral calculus, which would be expanded on by Newton and Leibniz. 3.4 Newton & Leibniz Sir Isaac Newton (1642-1727) was primarily concerned with Physics. For this reason, when he developed calculus, he did it in terms of time, that is, he considered how variables changed with time. While Newton considered how variables changed with time, Gottfried Wilhelm von Leibniz (1646-1716) was from a more pure side of maths and he developed calculus by thinking about how variables ranged over sequences that are infinitely close[2]. While Newton was quite flippant about the notation he used, Leibniz was very precise in the way he did everything, even down to his notation. It was himself that introduced the symbols dx and dy today is precisely because dy that are still commonly used today. The reason we use dx of Leibniz’ pedantry. This notation was carefully thought through, representing differences between successive sequences. As with those that came before them, Newton and Leibniz used infinitesimals. Since limits had not yet been introduced these were the most convenient for their calculations. There was, however, controversy about the use of infinitesimals. 9 3.5 Controversy Over Infinitesimals The problem with infinitesimals is that are not good for rigorously defining anything. This is because they do not really exist, in so much as that they can be manipulated easily into what you want. To illustrate the controversy, I will give an example. The definition of a derivative, as we now know, is f (x + h) − f (x) (3) f 0 (x) = lim h→0 h where f is a function, x is a variable and h is an infinitesimal (by which I mean that I am simulating it as an infinitesimal by sending it to zero). It is important to note that neither Newton nor Leibniz, or anyone else alive at that time for that matter, had this formula. For this simple example I will compute the derivative of f = x3 (x + h)3 − x3 h→0 h 3 x + 3x2 h + 3xh2 + h3 − x3 = lim h→0 h 3x2 h + 3xh2 + h3 = lim h→0 h 2 = lim 3x + 3xh + h2 f 0 (x) = lim (4) h→0 = 3x2 d 3 x = 3x2 ). What many people had a As we can clearly see this gives the correct result ( dx problem with however is the rôle that h plays. Up until the second to last line h is considered to be an ordinary, non-zero variable. However, on the second last line it supposed so small that it makes all terms containing it negligible. The use of limits redeems this inconsistency, however, before the introduction of limits, this was seen as a major problem in the work of Newton, Leibniz and anyone else working with them by many people, one of the most notable of whom was Berkeley. Lord Bishop George Berkeley (1685-1753) was a philosopher with an interest in maths who attacked the propagators of calculus [1] in his book “The Analyst: A Discourse Addressed to an Infidel Mathematician”. In it, he makes his reservations clear about infinitesimals or “ghosts of departed quantities”[9]. In fact, Berkeley’s criticisms were so well founded that it was not until very recently that infinitesimals were put on a rigorous foothold, namely in a book by the name of ’Non-Standard Analysis’ by Abraham Robinson[16]. In his book, Robinson introduces hyperreal numbers, ∗ R, whose main application is in non-standard analysis. An immediate consequence of hyperreal numbers is that the infinitesimal quantity can be rigorously defined. These criticisms about the foundations of calculus meant that it took a long time for it to be rigorously developed and widely accepted. 10 3.6 Cauchy & Weierstrass Augustin Louis Cauchy(1789 - 1857) had a profound impact on differential calculus. In his book “Course D’Analyse”, he gave what is believed to be the first appearance of the − δ definition[15]. This powerful definition provides a way to prove continuity of a curve which is very important for calculus since it is not possible differentiate a curve thatis not smooth. The definition states that, for any > 0, there exists some δ > 0 such that |x − x0 | < δ ⇒ |f (x) − f (x0 )| < (5) Another very important development in calculus was Cauchy’s proof of Taylor’s Theorem. This theorem allows one to express a function at a particular point in terms of it’s derivative and is an extremely powerful tool. One thing I feel I should point out here is the major contribution that Cauchy made to analysis with the Fundamental Theorem of Calculus[14]. As this is primarily about differentiation I will not discuss this in detail, however, it is one of the most fundamental and brilliant concepts in calculus and I feel I would be remiss without mentioning it. The reason that it is so important is because it relates differentials to integrals and, therefore, makes a link between differential and integral calculus. The Fundamental Theorem of Calculus states that for a continuous f on a closed interval [a, b] and with integral F , then Z b f (x)dx = F (b) − F (a) (6) a We know that Newton and Leibniz at least understood the concept of this theorem, however, they were not able to prove it. What the above theorem effectively states is that differentiation is the inverse of integration. Just as Cauchy did, Karl Weierstrass (1815-1897) attempted to put the work of Newton and Leibniz on a more rigorous footing. While it is believed that Cauchy first introduced the − δ definition formally to the world of maths, the proof he gave was not entirely correct. Cauchy proved it for pointwise convergence when he should have proved it for uniform convergence. Weierstrass realised the importance of this definition and proved it rigorously himself. The form of this definition given in equation (5) was presented by Weierstrass[15]. 11 4 4.1 Differential Calculus in the Curriculum History of Differential Calculus in the Leaving Certificate Between 1920 and 1960 there were very few changes in the Irish maths curriculum[21]. In fact, the syllabus remained quite stable after the free state was set up in 1922. The papers for the leaving certificate were divided in three sections. These were arithmetic, algebra & calculus and geometry & trigonometry. The calculus portion of the course included derivatives and integrals of elementary functions (Algebraic and Trigonometric) with easy applications to problems on rates, tangents, areas, volumes and to problems of motion[7]. It was during the 1960s that changes began to take place, with a new phase in the teaching of maths being implemented in 1964[20]. This new phase was put into motion in 1959 ”when the Department of Education sent a representative to the OEEC conference ’New Thinking In School of Mathematics’”[19]. For over 60 years the scope of leaving certificate maths was relatively limited. In 1964 there were many subjects added to the syllabus in order to give students a better grounding in maths education. Subjects added include sets, statistics & probability and vectors, among other things. To accommodate these new additions there were many aspects of the old course dropped, including certain theorems and troublesome calculations. This revision also meant that part of the calculus course began to be taught at lower levels[19]. During this revision it was decided that regular updates to the curriculum would be necessary and, accordingly, the next revision happened in the 1970s. During this decade matrices and linear transformations were added to the course whereas the areas of Taylor series and polar co-ordinates were reduced and moved to the applied maths course[21]. The maths course has always been a very long one. In many schools today students who are capable for the higher level opt to do pass instead because of the workload and this was no different back in the 1970s[21]. A proposed fix for this was to count a suitable higher level grade as the equivalent of two other courses. This was also done because universities wanted students who were better at maths. However, it was not just the universities. Employers were complaining that students failed were not able to perform basic arithmetic and blamed the course[21]. This led to a greater emphasis being put on algebraic manipulation and arithmetic calculation and a reduction in applications. The next, and outgoing, curriculum was the 1992 one. This course was still examined on two papers and had the following subjects: algebra, geometry, trigonometry, sequences & series, functions & calculus and discrete maths & statistics[3]. All of these were examined on paper 1 and section A of paper 2. There were also four options to choose from (further calculus & series, further probability & statistics, groups and further geometry) which were examined in section B of paper 2. With regard to calculus, the main change from the previous course was the introduction of the option, further calculus and series. Project Maths, which is quickly being introduced at the moment in the Irish curriculum, 12 is set to completely change the way the maths is taught and thought about in Irish schools. It is set to be completely functional in the junior certificate curriculum by 2015 and the leaving certificate curriculum by 2014. It is made up of five strands • Strand 1: Statistics and Probability • Strand 2: Geometry and Trigonometry • Strand 3: Numbers • Strand 4: Algebra • Strand 5: Functions with a large proportion of the weight stacked on the shoulders of Probability and Statistics. On first viewing the list of strands, none the words calculus, differentiation or integration appear. This led to a number of people believing that they went the were axed. Fortunately, this is not the case, as, if it were, it would be a tragedy of the highest proportions. In fact, calculus is tucked neatly into the fifth strand, the ambiguously named functions. The amount of calculus being taught, however, has reduced. The changes from the previous curriculum include • a reduction in first principle differentiation. Only linear and quadratic are to be examined, • proof of induction that d (xn ) dx = nxn−1 has been removed, • differentiation of implicit and parametric functions appears to have been removes also. As I have noted earlier the time that I spent in Alexandra College I observed the students struggling through exam-style questions. The life of a leaving certificate student (not only maths) is usually spent grappling with these type of questions, practicing for hours on end so when the right questions finally appear in the exam the student has three hours to regurgitate the numerous answers they have so painstakingly learned off. This is not what I consider learning and it is the type of approach that project maths is trying to eliminate. However, could they be going too far too fast? The authors of [12] claim that a complete reform of the system may be going too far. They claim that “there seemed to be far too much teaching to the exam rather than any actual learning of maths.” They suggest that it may be more efficient to make the teachers more skilled and reform the examination system. Personally, I tend to agree with the above view. I feel that project maths is an overreaction, a solution to the wrong problem, if you will, a mis-diagnosis. 13 5 Teaching Plan 5.1 Introduction In my lesson plan I am choosing to focus on differential calculus and I hope to cover most of the course here. I plan to teach a high level honours class differentiation. The way I am choosing to teach it is with rates of change by way of limits. I try not to go into too much detail where at all possible and I plan to cover as much relevant material as possible, including a review of functions at the beginning as they are very important for a course such as this. There is certain prior knowledge assumed for this course, namely that the students have covered all of the material in the junior cycle as well as geometry, trigonometry and functions in the senior cycle. My main resources for the teaching of this class will be the prescribed textbook and the past examination papers, however, how close I will stick to the textbook is still up for debate. As I have stated before I look to justify the calculus by the concepts of rates of change. Most of the class will be taught using the blackboard and the students are assumed to have the following attributes: Year 6th 5.2 Subject Mathematics: Higher Level Topic Differential Calculus Number of students 20 Characteristic of Class Able Class Length 45 minutes Lesson Plan1 Since strand 5 of project maths is not due to be implemented until the summer of 2014 I shall outline my lesson plan based on the syllabus of the previous incarnation, that is, the 1992 syllabus. 1 This lesson plan is based on notes given by [13] 14 Lesson 1 Review of linear, quadratic and cubic functions Lesson 2 Review of trigonometric, exponential and logarithmic functions Lesson 3 Limits Lesson 4 Limits at Infinity Lesson 5 Differentiation Lesson 6 Rate of Change and turning points Lesson 7 Maxima, minima and points of inflection Lesson 8 Derivatives of trigonometric, exponential and logarithmic functions Lesson 9 Product, quotient and chain rules Lesson 10 Implicit and parametric differentiation Lesson 11 In-class test 5.3 5.3.1 Unit Lesson 1 Prior Knowledge A basic knowledge of functions is assumed, although there will be a review so it does not have to be very in-depth. Content & Skills Graphs of constant, linear, quadratic and cubic functions. Principal Aim Student will understand the difference between a constant, linear, quadratic and cubic function. They will understand how each of these work and how to find points of intersection of functions like these. Behavioural Objectives At the end of the class, students should also be able to • draw a graph using a given function, • come up with their own conclusions from looking at a graph of a curve. Introduction The first thing to do is to make sure that the students understand the difference between a variable and a constant. I will begin by writing the functions f (x) = 2 and f (x) = x. In the interest of class participation I will open the floor to the meaning of these functions. I will explain that while the first function remains the same everywhere, the second one will change depending on the value of x. While this seems very basic, I view it as a necessary step since a lack of comprehension of what variables are can lead to many problems. 15 After giving an explanation I will draw each of the functions on the board so the students can get a visual representation of what is happening. From this it should be clear that f (x) = 2 will forever remain the same, while f (x) = x rises steadily and uniformly. In order to further illustrate the latter’s multi-valued nature I will plug in a few values of x to show how it changes. Development Presentation 1 On the blackboard write down f (x) = 2x. Question: What can we say about this curve? Application 1 Ask the students to consider a few different values of x and, hence, to draw the curve on graph paper. Ask them to compare their graph to the one drawn on the blackboard for f (x) = x. What do they notice? Presentation 2 On the blackboard write down f (x) = x2 . Again we find values of f (x) and plot these points. Do the same for f (x) = x2 + 1. Question: What are the similarities with these graphs? Application 2 Ask the students to do the same for the graphs f (x) = 2x2 and f (x) = 3x2 + 2. Explain to the students that these are called quadratic curves and that they always look like a parabola. Application 3 By now functions should be coming back. Ask students to look at cubic curves. The remainder of the class will be spent considering compositions of functions and intersection of functions. 5.3.2 Lesson 2 Prior Knowledge Basic trigonometry. Students should also know basic facts about the exponential and logarithmic functions. Content & Skills Graphs of trigonometric, exponential and logarithmic functions. Principal Aim The aim of this class is to review trigonometric, exponential and logarithmic functions. 16 Behavioural Objectives At the end of the class, the students should be able to: • recognise the graphs of the above functions, • draw and infer conclusions from these graphs. Introduction Today we want to review trigonometric functions, such as sin, cos and tan and the exponential and logarithmic functions. Development Presentation 1 I begin by drawing the graphs of sin x and cos x on the blackboard. We note that they both oscillate with the same period. I will quickly go over how sin and cos are defined using the unit circle. Application 1 I will ask the students to tell me specific values of sin x and cos x for certain values of x. We will also consider the C.A.S.T. diagram, that is, the one that gives the sign of sin, cos and tan in different quadrants. Presentation 2 Next we wish to look at tan. Again, I will go over the definition of tan and then proceed to graph it. If asymptotes have not been discussed before, this is the time to do it. I will show how tan x has an asymptote at x = nπ . 2 Application 2 As with sin and cos we will now look at different values of tan and how it behaves. Presentation 3 The final part of this class will be spent looking at the natural exponential and logarithm. Again, we graph the functions and we note that they are inverses of each other. The exponential has special properties, such as e0 = 1, ex > 0 and it is always increasing. We also know that it approaches zero as x approaches −∞ and it approaches ∞ as x approaches ∞. Log also has special properties like log 1 = 0. There is no need to discuss bases as we are only using the natural logarithm. Since ex = (log x)−1 , we have that elog x = x = log ex . 5.3.3 Lesson 3 Prior Knowledge Students should understand functions and be confident graphing them and inferring conclusions from graphs. 17 Content & Skills Limits Principal Aim In this lesson I want to successfully introduce the idea of limits and give some properties of them. Behavioural Objectives At the end of the class, the students should be able to: • compute limits of simple functions. Introduction In this class we want to consider the following question: If we have a function f (x), what happens when x gets close to some point a? Let’s look at this question with some examples. Development Presentation 1 Let’s take f (x) = 2x2 − x + 5 x+1 (7) and a = 1. As x approaches a, f (x) approaches 3. This value, f (a) = 3, is called the limit of the function f (x) at the point a. In other words, the limit of a function is the value it approaches at a certain point. We call this process taking a limit and, if our function is a polynomial, we can simply substitute this value into the function in order to find the limit at that point. In mathematical notation this looks like lim f (x) = f (a) x→a (8) Application 1 Evaluate the following limits: • f (x) = (x − 3)3 (9) f (x) = cos(x) (10) as x approaches a = 4. • as x approaches a = π. 18 Presentation 2 We now look to estimate x2 + 4x − 12 x→2 x2 − 2x lim f (x) = lim x→2 (11) Notice I say estimate. Solving this normally would yield zero in the denominator. Therefore, we look at what happens in the limit. x f (x) x f (x) 2.5 2.1 2.01 2.001 3.4 3.857 3.985 3.999 1.5 1.9 1.99 1.999 5.0 4.158 4.015 4.000 Subbing x = 2 straight into the equation is clearly not possible. Therefore, we have looked at values close to this point on either side of our curve. From this it should be clear that x2 + 4x − 12 lim =4 (12) x→2 x2 − 2x Explain that the function does not actually exist at x = 2. What we are doing above is considering what happens around this point. A limit does not care what happens at the point itself. At this stage it should be useful to look at some of the properties of limits. As with all operations in maths, limits have many properties. Firstly, limx→a c = c if c is a constant. We also have limx→a x = a and limx→a xn = an . Limits are linear. This means that limx→a [cf (x)] = c limx→a f (x) and limx→a [f (x) + g(x)] = limx→a f (x) + limx→a g(x). Hopefully this is straightforward enough as the students should have seen something similar before. We can do something similar for hproducts and quotients in this way: limx→a [f (x)g(x)] = i limx→a f (x) f (x) limx→a f (x) limx→a g(x) and limx→a g(x) = limx→a g(x) . Again, it is my hope that the students will be able to pick up on these without too much effort. It is probably necessary to give examples of all of these with figures after I state each property. 5.3.4 Lesson 4 Prior Knowledge Students should understand the basics of taking limits. Content & Skills Limits at infinity Principal Aim The aim of this lesson is to introduce limits at infinity. Behavioural Objectives At the end of the class, the students should be able to: • compute limits near zero and infinity. 19 Introduction As limits have been introduced, the next step is to consider limits at infinity. Development Presentation 1 To begin this class we look at functions that go to plus or minus infinity. These are called limits at infinity and they are very important. A function that takes the value of infinity at a is denoted lim f (x) = ∞ x→a (13) and a function that takes the value of minus infinity at a is denoted lim f (x) = −∞ x→a (14) To demonstrate this, look at the example 1 =∞ x→0 x lim (15) To see this, graph the function on the blackboard. We can see that as x gets smaller and smaller, the curve appears to get closer and closer to the y-axis. In fact it will never touch it. The y-axis here is known as the asymptote of the curve. Since the function never touches it, the value of f will approach infinity as x approaches 0. To further see this, look at f (x) for specific values of x: x f (x) 1 0.1 0.01 0.001 1 10 100 1000 We can see from that table that, as x decreases, f (x) increases. Now we shall consider what happens when x get bigger. Again, from the graph, it is clear that as x increases, f decreases. As before, we look at some specific points: x f (x) 1 10 100 1000 1 0.1 0.01 0.001 So, f gets smaller and smaller without touching the x-axis. We say that this axis is an asymptote to the curve. This shows us that limx→0 x1 = ∞. 20 Application 1 • Plot the function f (x) = 2 x−1 (16) • Evaluate the following limit 2 x→1 x − 1 lim (17) Does your graph correspond to the limit? Presentation 2 We now wish to look at more complex limits at infinity. For brevity I will do it here in variables rather than numbers. Let f (x) = a0 + · · · + an xn and g(x) = b1 + · · · + bn x n . What happens in the following limit? limx→∞ f (x). It would be tempting to simply plug in x = ∞. However, we can not do this. It leads to too much ambiguity. It will probably be important to explain this properly. The way we fix this is to factor out xn . This gives us f (x) = xn xan0 + · · · + an . Evaluating this limit yields limx→∞ f (x) = limx→∞ an xn , where f is defined as before. n (x) nx = limx→∞ ab00 +···a . We look to do the same as Next we consider limx→∞ fg(x) +···bn xn before, that is, factoring out xn . This leads to lim x→∞ f (x) g(x) xn = lim n x→∞ x = lim x→∞ = Similarly, limx→−∞ f (x) g(x) = a0 xn b0 xn · · · an · · · bn ! a0 · · · an xn b0 · · · bn xn ! an bn an . bn Conclusion Homework: • Evaluate limx→0 log x, • Evaluate limx→∞ x4 +x2 −2 , x−1 • Evaluate limx→−∞ x2 +1 . x3 −2x+1 Hint: To verify answers it is usually useful to graph functions. 21 (18) 5.3.5 Lesson 5 Prior Knowledge Limits Content & Skills Basic differentiation. Principal Aim I wish to introduce differentiation from first principles Behavioural Objectives At the end of the class, the students should be able to: • differentiate polynomials from first principles, • differentiate quotients from first principles. Introduction Today I will introduce the following limit f (x) − f (a) x→a x−a lim (19) This is called the derivative of a function f at the point a. The reason why we are looking at this limit in particular will be discussed in the next class. For now, however, it is important to see if one understands the idea of limits as they were introduced. We can rewrite the above equation in a more computationally friendly form. If we make the substitution x − a = h, we find that f (a + h) − f (a) h→0 h lim (20) Now, we have the following definition: The derivative of a function f at a point x is denoted f 0 (x) and is given by f (x + h) − f (x) h→0 h f 0 (x) = lim (21) This is called differentiating a function from first principles. Development Presentation 1 To see how this definition works we shall compute a few examples. Find the derivative of f (x) = 2x2 + 3x − 5 (22) 22 By the above definition, we have f (x + h) − f (x) h→0 h 2(x + h)2 + 3(x + h) − 5 − (2x2 + 3x − 5) = lim h→0 h 2x2 + 4xh + 2h2 + 3x + 3h − 5 − 2x2 − 3x + 5 = lim h→0 h 2 4xh + 2h + 3h = lim h→0 h = lim 4x + 2h + 3 f 0 (x) = lim (23) h→0 = 4x + 3 Therefore, the derivative of f (x) = 2x2 + 3x − 5 with respect to x is f 0 (x) = 4x + 3. This computation is the same for all polynomials. I would also like to introduce alternative notation. Recall that we can also write a function with y instead of f (x). The above equation would look like y = 2x2 + 3x − 5 in this dy form. Taking a derivative with respect to x is now denoted dx . It should be noted that this is the exact same as f 0 (x), just the notation is different. Application Find the derivative of the following polynomials: • f (t) = t2 − 5t − 2, • y = (x − 3)3 . Presentation 2 We will now consider a more complicated example. Recall from a previous class we considered the function f (x) = x1 . What is the derivative of this? 1 x+h − x1 f (x) = lim h→0 h 1 x − (x + h) = lim h→0 h x(x + h) 1 −h = lim h→0 h x(x + h) −1 = lim h→0 x(x + h) 1 =− 2 x 0 It is very important that the students understand all of the above steps. Application 2 Find the derivative of • g(x) = x . x+1 23 (24) Presentation 3 Recall the first few examples from this class. Is there any relation between the function and it’s derivative? Are there any conclusions we can make? If noone knows, do another example. We should eventually come to the conclusion that we can multiply by the power and then subtract one from the power. Explain that this only works for polynomials. Formally, if f is of the form xn , then it’s derivative is f 0 (x) = nxn−1 . Therefore, in the first example we can easily compute the derivative in this way. We have f (x) = 2x2 + 3x − 5. Looking at the first term in this function we get 2(2x2−1 ), by using the above rule, or 4x. The second term becomes 3x1−1 = 3. Note that constants become zero. Putting this together yields f 0 (x) = 4x + 3. Presentation 4 Finally I will differentiate f (x) = √ x: f (x + h) − f (x) h→0 h √ √ x+h− x = lim h→0 h √ √ √ √ x+h− x x+h+ x √ = lim √ h→0 h x+h+ x x+h−x = lim √ √ h→0 h( x + h + x) 1 = √ 2 x lim f (x) = lim h→0 (25) Note that this last calculation may overflow into the next class as it may need a more lengthly explanation. Conclusion Homework: Differentiate the following and confirm your answer by differentiating from first principles • f (x) = x3 − 2x2 + 3x − 4, • f (x) = (2x + 3)4 . Differentiate the following from first principles • g(x) = x+1 . x Remind the class about the rules of indices 5.3.6 Lesson 6 Prior Knowledge Slope from geometry Content & Skills Slope, rate of change and turning points. 24 Principal Aim The aim here is to consider practical uses of differentiation. We want to look at what differentiation means in maths. Behavioural Objectives At the end of the class, the students should be able to: • find the slope of a curve using differentiation, • compute turning points of a function. Introduction Differentiation has many applications in many areas of life and the idea of rates of change is one of the most important. First, we recall from geometry the formula for slope: m= f (x) − f (x1 ) x − x1 (26) where m is the slope and (x1 , f (x1 )), (x, f (x)) are points on the curve. To demonstrate this formula, I draw the graph of f (x) = x on the blackboard. I mark two arbitrary points and call them (x1 , f (x1 )), (x, f (x)). It will also be necessary to show where each point intersects the x- and y- axes. As we can see, the slope of this curve is the vertical distance divided by the horizontal distance. In other words, the slope can be described as the change in f (x) divided by the change in x. Using the above formula we find that, for f (x) = x, we have m= x − x1 x − x1 (27) =1 This tells us that our function changes at the same rate everywhere, which is the same with all linear functions. This is not an easy concept to grasp and it is, therefore, necessary to explain it fully. Development Presentation 1 We can use the above formula for slope, equation (26), to find how a function changes between two given points. Let’s look at this for a quadratic function, f (x) = 2x2 , say. We will try to find the slope of this curve at x1 = 3. By equation (26), 2x2 − 2x21 m= x − x1 (28) 2x2 − 18 = x−3 25 We can use this formula in order to find how f (x) changes between x = 3 and some other point on the line. What if we want to know how it changes at x = 3? This formula clearly will not work because, if we substitute x = 3 into (28), we find that m = 0. Drawing a rough diagram on the blackboard we can see that this is not the case. I mark the point x = 3 and we see that the slope is non-zero. If it was the curve would be constant at that point. What are we to do? Does anyone offer a suggestion? The formula for slope gives us the slope between two points. How can we incorporate this? What if we look for our second point to be as close to x = 3 as possible? Remind the class about the lesson on limits. What happens if we take a limit as x approaches 3? To do this we consider the slope between our point x and a point infinitesimally close to it. We call this point x + h, where h is an infinitesimal. Applying this gives us 2x2 − 2x21 m= x − x1 (29) 2(x + h)2 − 2x2 = x+h−x Since h is an infinitesimal we need to take the limit as h approaches 0, therefore 2(x + h)2 − 2x2 h→0 h f (x + h) − f (x) = lim h→0 h m = lim (30) Hopefully, the students will see that this is the same as the definition we have for the derivative. Therefore, the value of the derivative of a function at a point is the same as the slope at that point. Presentation 2 We can see from the graph of the function that before the y-axis it appears to be coming down while after the y-axis it appears to be going up, or, in other words, the function seems to be decreasing and then increasing. Recall from geometry that the slope can be found using trigonometry. We find it by taking the tan of the angle the function makes at a certain point with the x-axis. Therefore, if we take f (x) = x, we know that m = tan(45) = 1. If we take f (x) = −x, we know that m = tan(135) = −1. Note that the first function is always increasing, while the second function is always decreasing. Also note that the slope of the first function is positive and the slope of the second function is negative. This relation between the behaviour of a function and the sign of the slope, or derivative, always holds. That is, a function with a positive slope at a certain point is said to be increasing, while a function with a negative slope at a certain point is said to be decreasing. Returning to f (x) = 2x2 , we know that m = f 0 (x) = 4x. Taking x = 3, we find that f 0 (3) = 12, which is positive, therefore, the function is increasing at this point. Similarly, 26 if we take x = −2, we find that f 0 (x) = −8, which is negative, therefore, the function is decreasing at this point. Presentation 3 This is all very good but we must now consider what happens at the origin. Note that as the graph cuts the y-axis the function stops decreasing and starts increasing. This is called a turning point. It is important because it is a transition point. What is interesting is that at x = 0 the function becomes constant and, therefore, the derivative is zero. It is not difficult to understand why the function is constant at a turning point. To get from the decreasing part to the increasing part it must flatten out somewhere. In our example this happens at x = 0. To see this we want to find the point where the slope is equal to 0. Since the slope is the same as the derivative we differentiate our function and set it equal to 0. Doing this we find that 4x = 0, which implies x = 0. In order to find the exact turning point we need a second co-ordinate. Subbing x = 0 into f (x) = 2x2 gives us that co-ordinate. Therefore, we now know that we have a turning point at (0, 0). Application The rest of the class will be spent looking at turning points of functions. 5.3.7 Lesson 7 Prior Knowledge Turning points and differentiation. Content & Skills Maxima and minima and points of inflection. Principal Aim In this lesson I want to introduce the idea of maxima and minima of a curve and points of inflection. I also want to discuss how to sketch a graph using this information. Behavioural Objectives At the end of the class, the students should be able to: • find the local maxima and minima of a function, • find the point of inflection of a function, • determine where a function is increasing and decreasing • sketch functions using the above information. 27 Introduction Recall from the last lesson we saw how to find the turning points of a function. In this lesson we will see a practical use for these turning points, namely we will see how to find local maxima and minima of a function. What do I mean by maximum and minimum. A function has a maximum at the point where it has the greatest value on the y-axis. Similarly, a function has a minimum at the point where it has the lowest value on the y-axis. Development Presentation 1 Recall that a turning point is found by finding where the derivative is zero. Let’s take f (x) = 2x3 + 3x2 − 12x + 4. Therefore, f 0 (x) = 6x2 + 6x − 12. This function has two turning points, namely (1, −3) and (−2, 24). This function has a maximum at (−2, 24) and a minimum at (1, −3). How do we know that this is true? Do we not have to check all points? We know that these are right because maxima and minima can only occur at turning points. What are the maxima and minima of f (x) = 1/4x4 + 2/3x3 − 1/2x2 − 2x − 1/12? We have three turning points: (−2, 7/12), (−1, 1) and (1, −5/3). From this we see that we have a minimum at the point (1, −5/3). However, what is our maximum? It is the one that takes the highest value on the y-axis, namely (−1, 1). Application 1 Find the maxima and minima of the following functions: • f (x) = x3 − 2x2 + 1, • f (t) = t5 + t4 − 3t3 + 1. Presentation 2 First derivatives are very useful. They can give us lots of information about out function. We can use the first derivative, for example, to tell if our function is increasing, decreasing, or neither. What do these words mean in maths? If x1 < x2 , we say f is increasing if f (x1 ) < f (x2 ) and we say f is decreasing if f (x1 ) > f (x2 ). If we take the above example f (t) = t5 + t4 − 3t3 + 1, we find that the turning points are (0, 1), (1, 0) and (− 59 , 10). This tell us that it is increasing on (−∞, − 95 ) and (1, ∞) and decreasing on (− 95 , 1). Application 2 Find where f (x) = x3 − 2x2 + 1 is increasing and decreasing. Presentation 3 We are now able to sketch graphs. I will demonstrate this by sketching f (x) = x3 − 2x2 + 1 using turning points and its increasing and decreasing properties. Application 3 Sketch the graph of f (t) = t5 + t4 − 3t3 + 1. 28 Presentation 4 We now wish to look at points of inflection. These are where the direction of the curve changes. At these points the second derivative is zero. To demonstrate this consider f (x) = x3 . We find that f 00 (x) = 6x. This is zero when x = 0. Looking at the graph of the curve we see that at the origin it moves from being concave shape to a convex shape. This leads us to the following. A function, f , is called concave at a point a if f 00 (a) < 0 and it is called convex at a if f 00 (a) > 0. Application 4 Determine where f (x) = x4 − x2 + 1 is concave and convex. The rest of the class will be taken up doing real life examples such as: a population is modelled by the function f (t) = t2 log(3t) + 6. After how long will it start to increase? 5.3.8 Lesson 8 Prior Knowledge Trigonometric, exponential and logarithmic functions, limits and the definition of the derivative. Content & Skills Trigonometric, exponential and logarithmic functions. Principal Aim We wish to look at the derivatives of trigonometric, exponential and logarithmic functions. Behavioural Objectives At the end of the class, the students should be able to: • differentiate trigonometric, exponential and logarithmic functions. Introduction We wish to use the definition of the derivative to differentiate certain special functions. Development Presentation 1 We will derive the derivatives of sin(x) and cos(x). We first take f (x) = sin(x) f (x + h) − f (x) h→0 h sin(x + h) − sin(x) = lim h→0 h (31) sin(x) cos(h) + cos(x) sin(h) − sin(x) = lim h→0 h sin(x) cos(h) − sin(x) cos(x) sin(h) = lim + h→0 h h At this point I will tell the class to note that the first fraction can be written as follows f 0 (x) = lim 29 sin(x)(cos(h) − 1) sin(x) cos(h) − sin(x) = lim h→0 h→0 h h =0 lim (32) We now wish to consider sin(h) for small h. The best way to understand this is to plot h it. It should be clear from the graph that the function reaches a maximum at f (0) = 1 and then goes to zero at ±∞. Therefore, we can conclude that limh→0 cos(x)hsin(h) = cos(x). So, from first principles, we can clearly see that the derivative of sin(x) is cos(x). We will proceed to compute the derivative of cos(x) and show that it is − sin(x). sin(x) . We should find that We now look to compute the derivative of f (x) = tan(x) = cos(x) f 0 (x) = cos12 (x) Presentation 2 We look at f (x) = ax . Working this down, we find that ah − 1 f (x) = a lim h→0 h 0 x = f (0)a 0 x (33) This gives us a problem. In order to compute the derivative we need the derivative. Remind the students about the exponential function. I give the following definition that they will not have seen before: eh − 1 =1 (34) lim h→0 h This tells us that the derivative of the exponential is itself. Now, we recall the natural logarithm, log x, the derivative of which is x1 . Application The rest of the class will be spent computing derivatives of the above types of functions. 5.3.9 Lesson 9 Prior Knowledge The students should know how to compute derivatives. Content & Skills Product, quotient and chain rule. Principal Aim In this class we wish to look at how to compute derivatives of more complex functions. Behavioural Objectives At the end of the class, the students should be able to: • Implement the product rule, 30 • Implement the quotient rule, • Implement the chain rule. Introduction We now have a few ways to compute derivatives of functions. We can do it by first principles or we can use the formula for polynomials. However, this leaves many functions very difficult to differentiate. First principles can get very tricky and the latter can only be used for polynomials. Today we will consider how to differentiate more complex functions. Development Presentation 1 Today we will look at differentiation a little closer. Consider the functions f (x) = x2 and g(x) = x3 . We can multiply these to find that (f g)(x) = x5 . Differentiating we get (f g)0 (x) = 5x4 . Now, we try f 0 (x)g 0 (x) = (2x)(3x2 ) = 6x3 . We can clearly see that (f g)0 (x) 6= f 0 (x)g 0 (x), that is, the derivative of a product is not the product of a derivative. 0 3 2 = xx2 . We now find that fg 0(x) = 3x 6= 1 = The same is true for quotients. Taking fg(x) (x) (x) 2x f 0 ( g ) (x). In order to differentiate these properly we use the product and quotient rules. The product rule for two functions, f (x) and g(x), is (f g)0 (x) = f 0 (x)g(x) + f (x)g 0 (x) (35) The quotient rule for two functions, f (x) and g(x) 6= 0, is 0 f f 0 (x)g(x) − f (x)g 0 (x) (x) = g g(x)2 (36) We now look at some examples. Take f (x) = x and g(x) = ex . What is (f g)0 (x)? We use the product rule to get ex (1 + x). What if we want f g 0 (x)? In this case we use the quotient rule and get ex (1−x) e2x = 1−x . ex Application 1 This is an important concept and also one that students tend to have trouble with. Therefore, it is necessary to do many examples. Presentation 2 Recall from a few classes ago we looked at the example f (x) = (x−3)3 . This was computed from first principles, however, it is not a very nice calculation as there are many terms. For higher powers computing a derivative this way becomes ridiculous. For 31 this reason there is a formula to deal with functions such as these. It is called the chain rule. Explain how the chain rule works and what functions it is useful to use it for. Differentiate f (x) = (x − 3)3 by the chain rule. f 0 (x) = 3(x − 3)3−1 = 3(x − 3)2 (37) Does this correspond with what we got earlier? Application 2 As before, this is a very important concept and plenty of examples are necessary. 5.3.10 Lesson 10 Prior Knowledge Differentiation, product rule Content & Skills Implicit and parametric differentiation. Principal Aim In this class we want to look at how to differentiate implicitly and parametrically. Behavioural Objectives At the end of the class, the students should be able to: • differentiate implicitly, • differentiate parametrically. Introduction The first thing to do is to remind the class about the notation we used previously, that is, using y instead of f (x) as our function. Up until now we looked at functions of the form y = f (x). Now we want to look what happens when out x’s and y’s are not split up. Development Presentation 1 We will begin with an example: x + xy = 1. We want to differentiate this with respect to x. There are two ways to do this. The first way is to rewrite the equation dy . in a form we already know, that is, y = 1−x . Therefore, dx = −1 x x2 The second method is to use implicit differentiation. We look to differentiate term by d term. The first term we have seen before, dx x = 1. The second term is more difficult. We need to use the product rule where f (x) = x and g(x) = y. By the product rule, we get dy dy dy dy x dx + y. Putting this together gives 1 + x dx + y = 0. Solving for dx gives dx = y−1 . Subbing x 1−x in y = x gives dy 1 =− 2 (38) dx x 32 which is the same as we got before. Although it is possible to avoid using implicit differentiation here, there are many situation where it is necessary. Application 1 We want to look at some examples. Differentiate the following implicitly: • 2x2 y 2 − xy 5 = x, • x sin y + y cos x = 0. dy d (n) y (x) = ny (n−1) (x) dx , where y (n) (x) is the nth derivative of y with respect We note that dx to x, which is the chain rule. Presentation 2 In the second half of this class we will look at parametric differentiation. Firstly, what does the word parametric mean. Until now x has not depended on anything else. This means that we can not write x in terms of any other variable. We also had, until this class, that y has not depended on anything. What if x and y depend on the same variable, t, say. By this I mean x = x(t) and y = y(t). This is best illustrated by an example. dy . We do this by finding dx = 2t and Take x = t2 − 2 and y = t + 1. The idea is to find dx dt dy dy 2t = 1. Expressing the first as a quotient of the second gives dx = 1 = 2t. dt Application 2 Look at examples • x = cos t and y = sin t, • x = tet and y = t2 + t. 33 References [1] Ghosts of departed quantities: Calculus and it’s limits. [2] History@ONLINE. [3] Leaving cert syllabus. [4] Method of Exhaustion. [5] Method of Exhaustion@ONLINE. [6] The Rise of Calculus@ONLINE. [7] Brainse an Mhe n-Oideachais An Roinn Oideachais. Programme and regulations regarding curricula, certifications, examinations and scholarships. 1924. [8] Aristotle. Physics. [9] George Berkeley. The Analyst: A Discourse Addressed to an Infidel Mathematician. [10] Carl Boyer. History of Mathematics. [11] Scott E. Brodie. An ancient extra-geometric proof. [12] J. J. Grannell, P. D. Barry, M. Cronin, F. Holland, D. Hurley. Interim report on project maths. [13] Paul Dawkins. Calculus i - notes. [14] Karen E. Donnelly. Cauchy and the rigorous development of calculus@ONLINE. [15] Judith V. Grabiner. Who gave you the epsilon? cauchy and the origins of rigorous calculus. [16] H. Jerome Keisler. Elementary Calculus: An Infinitesimal Approach. [17] Jim Loy. Zeno’s paradoxes. [18] The MacTutor History of Mathematics archive. Greek number systems. [19] Elizabeth Oldham. Irish curriculum changes 1959-1979. [20] Elizabeth Oldham. Second iea mathematics survey. 1964. [21] Elizabeth Oldham. Second iea mathematics survey. 1976. 34
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