#3
Exponential Functions
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
Quick Review
In Exercises 1- 3, evaluate the expression. Round your answers
to 3 decimal places.
2
3
1.
5
3.
3- 1.5
2.
3
2
In Exercises 4 - 6, solve the equation. Round your answers
to 4 decimal places.
4.
x 3 = 17
6.
x10 = 1.4567
5.
x 5 = 24
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
Slide 1- 2
Quick Review
In Exercises 7 and 8, find the value of investing P dollars for
n years with the interest rate r compounded annually.
7.
P = $500,
r = 4.75%,
n = 5 years
8.
P = 1000,
r = 6.3%,
n = 3 years
In Exercises 9 and 10, simplify the exponential expression.
2
9.
(x - 3 y 2 )
3 3
(x y )
4
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
2
- 1
4 - 2ö
æa 3b- 2 ö
æ
a
c ÷
÷
ç
ç
10. ç 4 ÷
÷
÷
çè c ø
÷ èçç b3 ø÷
÷
Slide 1- 3
Quick Review Solutions
In Exercises 1 - 3, evaluate the expression. Round your answers
to 3 decimal places.
2
3
1.
5
3.
3- 1.5
2.924
2.
3
2
4.729
0.192
In Exercises 4 - 6, solve the equation. Round your answers
to 4 decimal places.
4.
x 3 = 17
6.
x10 = 1.4567 ± 1.0383
2.5713
5.
x 5 = 24
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
1.8882
Slide 1- 4
Quick Review Solutions
In Exercises 7 and 8, find the value of investing P dollars for
n years with the interest rate r compounded annually.
7.
P = $500,
r = 4.75%,
n = 5 years
$630.58
8.
P = 1000,
r = 6.3%,
n = 3 years
$1201.16
In Exercises 9 and 10, simplify the exponential expression.
9.
2 2
(x y )
4 3 3
x
( y)
- 3
1
x18 y 5
2
- 1
æa 3b- 2 ö
æa 4 c- 2 ö÷
÷
çç
10. çç 4 ÷
÷
÷
çè c ø
÷ èç b3 ø÷
÷
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
a2
bc 6
Slide 1- 5
What you’ll learn about…




Exponential Growth
Exponential Decay
Applications
The Number e
…and why
Exponential functions model many growth
patterns.
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
Slide 1- 6
Exponential Function
Let a be a positive real number other than 1. The function
f ( x) = a x
is the exponential function with base a.
The domain of f ( x) = a x is (- ¥ , ¥ ) and the range is (0, ¥ ).
Compound interest investment and population growth are examples
of exponential growth.
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
Slide 1- 7
Exponential Growth
If a 1 the graph of f looks like the graph
of y= 2 x in Figure 1.22a
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
Slide 1- 8
Exponential Growth
If 0  a 1 the graph of f looks like the graph
of y = 2- x in Figure 1.22b.
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
Slide 1- 9
Rules for Exponents
If a > 0 and b > 0, the following hold for all real numbers x and y.
x
1. a x ×a y = a x + y
4. a x ×b x = (ab)
ax
2. y = a xa
x
æa ö
a
5. çç ÷
÷
÷ = bx
çè b ø
3. (a
x
y
x
y
y x
) = (a ) = a xy
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
Slide 1- 10
Half-life
Exponential functions can also model phenomena that produce
decrease over time, such as happens with radioactive decay.
The half-life of a radioactive substance is the amount of time it
takes for half of the substance to change from its original
radioactive state to a non-radioactive state by emitting energy
in the form of radiation.
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
Slide 1- 11
Exponential Growth and Exponential Decay
The function y = k ×a x , k > 0, is a model for exponential growth
if a > 1, and a model for exponential decay if 0 < a < 1.
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
Slide 1- 12
Example Exponential Functions
Use a grapher to find the zero's of f (x)= 4x - 3.
f (x)= 4 x - 3
[-5, 5], [-10,10]
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
Slide 1- 13
The Number e
Many natural, physical and economic phenomena are best modeled
by an exponential function whose base is the famous number e, which is
2.718281828 to nine decimal places.
x
æ 1÷
ö
ç
We can define e to be the number that the function f (x )= ç1 + ÷
çè x ÷
ø
approaches as x approaches infinity.
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
Slide 1- 14
The Number e
The exponential functions y = e x and y = e- x are frequently used as models
of exponential growth or decay.
Interest compounded continuously uses the model y = P ×e r t , where P is the
initial investment, r is the interest rate as a decimal and t is the time in years.
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
Slide 1- 15
Example The Number e
The approximate number of fruit flies in an experimental population after
t hours is given by Q (t )= 20 e 0.03 t ,
t ³ 0.
a. Find the initial number of fruit flies in the population.
b. How large is the population of fruit flies after 72 hours?
c. Use a grapher to graph the function Q.
a. To find the initial population, evaluate Q (t ) at t = 0.
Q (0)= 20e
0.03(0)
= 20e0 = 20 (1)= 20 flies.
b. After 72 hours, the population size is
Q (72)= 20e
0.03(72)
= 20e 2.16 » 173 flies.
c.
Q(t )= 20e0.03t , t ³ 0
[0,100] by [0,120] in 10’s
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Prentice Hall
Slide 1- 16