Secondary 2
Chapter 3/4
Secondary II
Unit 3 – Properties of Triangles
Unit 4 – Similarity through Transformations
Date
Section Assignment
2014/2015
Concept
A: 9/23
B: 9/24
3.1/3.2
- Worksheet 3.1 & 3.2
Triangle Sum, Exterior Angle, and
Exterior Angle Inequality
Theorems
The Triangle Inequality Theorem
A: 9/25
B: 9/26
3.3/3.4
- Worksheet 3.3 & 3.4
Properties of a 45-45-90 Triangle
Properties of a 30-60-90 Triangle
A: 9/29
B: 9/30
4.1/4.2
- Worksheet 4.1 & 4.2
Dilating Triangles to Create Similar
Triangles
Similar Triangle Theorems
A: 10/1
B: 10/2
4.3/4.4
- Worksheet 4.3 & 4.4
Theorems About Proportionality
More Similar Triangles
A: 10/3
B: 10/6
4.5/4.6
- Worksheet 4.5 & 4.6
Proving the Pythagorean Theorem
and the Converse P. Theorem
Application of Similar Triangles
A: 10/7
B: 10/8
Review Worksheet
A: 10/9
B: 10/10
Chapter 3/4 TEST
Late and absent work will be due on the day of the review (absences must be excused). The review assignment
must be turned in on test day. All required work must be complete to get the curve on the test.
Remember, you are still required to take the test on the scheduled day even if you miss the review, so come
prepared. If you are absent on test day, you will be required to take the test in class the day you return. You will not
receive the curve on the test if you are absent on test day unless you take the test prior to your absence.
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Secondary 2
Chapter 3/4
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Secondary 2
Chapter 3/4
Chapter 3/4: Probability and Counting
3.1/3.2 – Triangle Sum, Exterior Angle, Exterior Angle Inequality, and Triangle inequality Theorems
The Triangle Sum Theorem states: The sum of the measures of the interior angles of a triangle is 180°.
Example 1: Draw an acute scalene triangle. Use a protractor to measure each interior angle and label the
angles measures.
1. Measure the length of each side of the triangle. Label the sides in your diagram.
2. Which interior angle is opposite the longest side of the triangle?
3. Which interior angle lies opposite the shortest side of the triangle?
Example 2: List the sides from shortest to longest in each diagram.
a.
b.
c.
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Chapter 3/4
Example 3: Use the diagram shown to answer the following questions.
1. Name the interior angles of the triangle.
2. Name the exterior angles of the triangle.
3. What does 𝑚∠1 + 𝑚∠2 + 𝑚∠3 equal? Explain.
4. What does 𝑚∠3 + 𝑚∠4 equal? Explain.
5. Why does 𝑚∠1 + 𝑚∠2 = 𝑚∠4?
The remote interior angles of a triangle are the two angles that are non-adjacent to the specified exterior
angle.
The Exterior Angle Theorem states: The measure of the exterior angle of a triangle is equal to the sum of the
measures of the two remote interior angles of a triangle.
Example 4: Solve for x in each diagram.
a.
b.
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Chapter 3/4
c.
d.
The Exterior Angle Inequality Theorem states: The measure of the exterior angle of a triangle is greater
than the measure of either of the remote interior angles of the triangle.
Example 4: In groups, roll a dice 3 times to get values for three potential sides of a triangle. Write each of the
three rolls on the chart below. Once you have written them down, using a ruler and the space below,
determine whether the three sides form a triangle.
Roll 1
Roll 2
Roll 3
Forms a triangle?
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Secondary 2
Chapter 3/4
1. Compare the lengths that formed a triangle with the ones that did not. What you do notice?
2. Under what conditions were you able to form a triangle?
3. Under what conditions were you unable to form a triangle?
Example 5: Determine if it is possible to form a triangle using segments with the following measurements.
Explain your reasoning.
a. 2 cm, 5.1 cm, 2.4 cm
b. 9.2 cm, 7 cm, 1.9 cm
The Triangle Inequality Theorem states: The sum of the lengths of any two sides of a triangle is greater than
the length of the third side.
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Secondary 2
Chapter 3/4
Additional Notes
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Secondary 2
Chapter 3/4
3.3/3.4 – Properties of 45-45-90 and 30-60-90 Triangles
Rationalizing the Denominator
Square roots are NOT in simplest form when there is a square root in the denominator. Rationalizing the
denominator is the process used to get rid of the square root in the denominator. To do this, simplify the
square root, and then multiply the numerator and denominator by the simplified square root.
Example 1: Simplify the following radicals.
a.
c.
1
2
1
3
b.
2 15
3
d.
3
2√5
You will frequently need to determine the value of trigonometric ratios for 30 - 60 , and 45 angles. In
Trigonometry we study the 30  60  90 special triangle and the 45  45  90 special triangle.
Simplest Side Ratios for Special Right Triangles
30°
45°
2
√3
1
√2
60°
45°
1
1
Example 1: Find the missing sides using the 45  45  90 Special Right Triangles.
a.
b.
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Chapter 3/4
c.
d.
e.
1. Explain how you calculate the length of the hypotenuse given a leg.
2. Explain how you calculate the length of the side given the hypotenuse.
Example 2: Find the missing sides using the 30  60  90 Special Right Triangles.
a.
d.
b.
e.
c.
f.
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Secondary 2
Chapter 3/4
Explain how you calculate the following on a 30  60  90 triangle:
1. The length of the hypotenuse given the length of the shorter leg.
2. The length of the hypotenuse given the length of the longer leg.
3. The length of the shorter leg given the length of the longer leg.
4. The length of the shorter leg given the length of the hypotenuse.
5. The length of the longer leg given the length of the shorter leg.
6. The length of the longer leg given the length of the hypotenuse.
Example 3: Find the missing side using the Special Right Triangles.
a.
b.
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Secondary 2
Chapter 3/4
Additional Notes
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Secondary 2
Chapter 3/4
4.1/4.2 – Dilating Triangles to Create Similar Triangles, and Similar Triangle Theorems
Example 1: Redraw the given figure such that it is twice its size.
1. When you redrew the figure, did the shape of the figure change?
2. When you redrew the figure, did the size of the figure change?
3. How did you get the measurements for the redrawn figure?
4. What is the ratio of the short side of the smaller figure to the short side of the larger figure?
5. What is the ratio of the long side of the smaller figure to the long side of the larger figure?
6. What do you notice about the ratios?
7. What do you notice about the corresponding angles in each of the figures?
8. What is the relationship between the image and pre-image?
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Secondary 2
Chapter 3/4
Because the second figure was twice as big as the given figure, it is considered to have a dilation factor of 2.
Similar Triangles are triangles that have all pairs of corresponding angles congruent and all corresponding
sides proportional. Similar triangles have the same shape but not always the same size.
Example 2: Triangle 𝐽′𝐾′𝐿′ is a dilation of ∆𝐽𝐾𝐿. The center of the dilation is the origin.
1. List the coordinates of the vertices of ∆𝐽𝐾𝐿 and ∆𝐽′𝐾′𝐿′.
How do the coordinates of the image compare to the
coordinates of the pre-image?
2. What is the scale factor of the dilation? Explain.
3. How do you think you can use the scale factor to determine the coordinates of the vertices of an
image?
4. Use coordinate notation to describe the dilation of point (𝑥, 𝑦) when the center of the dilation is at
the origin using a scale factor of k.
Example 3: Triangle 𝐻𝑅𝑌 ~ Triangle 𝐽𝑃𝑇. Draw a diagram that illustrates this similarity statement and list
all of the pairs of congruent angles and all of the proportional sides.
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Chapter 3/4
Example 4: What conditions are necessary to show triangle GHK is similar to triangle MHS?
The Angle-Angle Similarity Theorem states: If two angles of one triangle are congruent to two angles of
another triangle, then the triangles are similar.
If 𝑚∠𝐴 = 𝑚∠𝐷 and 𝑚∠𝐶 = 𝑚∠𝐹, then ∆𝐴𝐵𝐶~∆𝐷𝐸𝐹.
Example 5: The triangles shown are isosceles triangles. Do you have enough information to show that the
triangles are similar? Explain your reasoning.
Example 6: The triangles shown are isosceles triangles. Do you have enough information to show that the
triangles are similar? Explain your reasoning.
The Side-Side-Side Similarity Theorem state: If all three corresponding sides of two triangles are
proportional, then the triangles are similar.
If
𝐴𝐵
𝐷𝐸
𝐵𝐶
𝐴𝐶
= 𝐸𝐹 = 𝐷𝐹 , 𝑡ℎ𝑒𝑛 ∆𝐴𝐵𝐶~∆𝐷𝐸𝐹.
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Chapter 3/4
Example 6: Determine whether ∆𝑈𝑉𝑊 is similar to ∆𝑋𝑌𝑍. If so, use symbols to write a similarity statement.
An included angle is formed by two consecutive sides of the figure.
An included side is a line segment between two consecutive angles.
The Side-Angle-Side Similarity Theorem states: If two of the corresponding sides of two triangles are
proportional and the included angles are congruent, then the triangles are similar.
𝐴𝐵
𝐴𝐶
If 𝐷𝐸 = 𝐷𝐹 and ∠𝐴 ≅ ∠𝐷, then ∆𝐴𝐵𝐶~∆𝐷𝐸𝐹.
Example 6: Determine whether the pair of triangles are similar. Explain your reasoning.
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Chapter 3/4
Additional Notes
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Chapter 3/4
4.3/4.4 – Theorems about Proportionality and More Similar Triangles
The Angle Bisector/Proportional Side Theorem states: A bisector of an angle in a triangle divides the
opposite side into two segments whose lengths are in the same ratio as the lengths of the sides adjacent to
the angle.
𝐴𝐵
𝐵𝐷
If 𝐴𝐷 bisects ∠𝐵𝐴𝐶, then 𝐴𝐶 = 𝐶𝐷
Example 1: On the map shown, North Craig Street bisects the angle formed between Bellefield Avenue and
Ellsworth Avenue.



The distance from the ATM to the Coffee Shop is 300 feet.
The distance from the Coffee Shop to the Library is 500 feet.
The distance from your apartment to the Library is 1200 feet.
1. Determine the distance from you apartment to the ATM.
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Secondary 2
Chapter 3/4
Example 2:
𝐶𝐷 bisects ∠𝐶. Solve for DB.
Example 3:
𝐶𝐷 bisects ∠𝐶. Solve for AC.
Example 4:
𝐴𝐷 bisects ∠𝐴. 𝐴𝐶 + 𝐴𝐵 = 36. Solve for AC and AB.
Example 5:
𝐵𝐷 bisects ∠𝐵. Solve for AC.
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Chapter 3/4
The Triangle Proportionality Theorem states: If a line parallel to one side of a triangle intersects the other
two sides, then it divides the two sides proportionally.
If 𝐵𝐶 is parallel to 𝐷𝐸, then
Example 6:
𝐵𝐷
𝐷𝐴
=
𝐶𝐸
.
𝐸𝐴
Use the Triangle Proportionality Theorem to determine the missing value.
The Converse of the Triangle Proportionality Theorem states: If a line divides the two sides of a triangle
proportionally, then it is parallel to the third side.
𝐵𝐷
𝐶𝐸
If 𝐷𝐴 = 𝐸𝐴 , then 𝐵𝐶 is parallel to 𝐷𝐸.
The Proportional Segments Theorem states: If three parallel lines intersect two transversals, then they
divide the transversals proportionally.
If 𝐿1 ∥ 𝐿2 ∥ 𝐿3 , then
𝐴𝐵
𝐵𝐶
=
𝐷𝐸
.
𝐸𝐹
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Secondary 2
Example 6:
Chapter 3/4
Use the Proportional Segments Theorem to determine the missing value.
The Triangle Midsegment Theorem states: The midsegment of a triangle is parallel to the third side of the
triangle and is half the measure of the third side of the triangle.
1
2
If JG is the midsegment of the triangle, then 𝐽𝐺 ∥ 𝐷𝑆 , and 𝐽𝐺 = 𝐷𝑆.
Example 7: Ms. Zoid asked her students to determine whether 𝑅𝐷 is a midsegment of ∆𝑇𝑈𝑌, given
𝑇𝑌 = 14 𝑐𝑚 and 𝑅𝐷 = 7 𝑐𝑚. Carson told Alicia that using the Midsegment Theorem, he could conclude that
𝑅𝐷 is a midsegment. Is Carson correct? Explain.
Example 8: Ms. Zoid drew a second diagram on the board and asked her students to determine if 𝑅𝐷 is a
midsegment of ∆𝑇𝑈𝑌, given 𝑅𝐷 ∥ 𝑇𝑌. Alicia told Carson that using the Midsegment Theorem, she could
conclude that 𝑅𝐷 is a midsegment. Is Alicia correct? Explain.
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Secondary 2
Chapter 3/4
The altitude of a triangle is the line segment drawn to a vertex of a triangle perpendicular to the line
containing the opposite side.
𝐶𝐷 is the altitude of 𝐴𝐵.
The Right Triangle Altitude Similarity Theorem states: If an altitude is drawn to the hypotenuse of a right
triangle, then the two triangle formed are similar to the original triangle and to each other.
If 𝐶𝐷 is the altitude of 𝐴𝐵, then ∆𝐴𝐵𝐶~∆𝐴𝐶𝐷~∆𝐶𝐵𝐷.
𝑎
𝑥
The geometric mean of two positive numbers a and b is the positive number x such that 𝑥 = 𝑏
The Right Triangle Altitude/Hypotenuse Theorem states: The measure of the altitude drawn from the
vertex of the right angle of a right triangle to its hypotenuse is the geometric mean between the measures
of the two segments of the hypotenuse.
If 𝐶𝐷 is the altitude of 𝐴𝐵, then
𝐴𝐷
𝐶𝐷
=
𝐶𝐷
.
𝐵𝐷
The Right Triangle Altitude/Leg Theorem states: If the altitude is drawn to the hypotenuse of a right
triangle, each leg of the right triangle is the geometric mean of the hypotenuse and the segment of the
hypotenuse adjacent to the leg.
𝐴𝐶
𝐶𝐷
If 𝐶𝐷 is the altitude of 𝐴𝐵, then 𝐶𝐷 = 𝐶𝐵.
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Chapter 3/4
Example 9: Solve for x in each triangle below.
a.
b.
c.
d.
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Secondary 2
Chapter 3/4
Additional Notes
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Secondary 2
Chapter 3/4
4.5/4.6 – Proving the Pythagorean Theorem and its Converse, Application of Similar Triangles
Example 1: Use the Right Triangle/Altitude Similarity theorem to prove the Pythagorean Theorem.
Given: Triangle ABC with right angle C
Prove: 𝐴𝐶 2 + 𝐶𝐵2 = 𝐴𝐵2
1. Construct altitude CD to hypotenuse CD.
2. Applying the Right Triangle/Altitude Similarity Theorem, what can you conclude?
3. Write a proportional statement describing the relationship between the longest leg and
hypotenuse of triangle ABC and triangle CBD.
4. Rewrite the proportional statement you wrote in Question 3 as a product.
5. Write a proportional statement describing the relationship between the shortest leg and
hypotenuse of triangle ABC and triangle ACD.
6. Rewrite the proportional statement you wrote in Question 5 as a product.
7. Add the statement in Question 4 to the statement in Question 6.
8. Factor the statement in Question 7.
9. What is equivalent to 𝐷𝐵 + 𝐴𝐷?
10. Substitute the answer to Question 9 into the answer in Question 8 to prove the Pythagorean
Theorem.
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Chapter 3/4
Example 2: You go to the park and gather enough information to calculate the height of one of the trees. The
figure shows your measurements. Calculate the height of the tree.
Example 3: Stacey lines herself up with the tree’s shadow so that the tip of her shadow and the tip of the
tree’s shadow meets. A diagram is shown below. Calculate the height of the tree.
Example 4: You stand on one side of the creek and your friend stands directly across the creek from you on
the other side as shown in the figure. Your friend is standing 5 feet from the creek and you are standing 5 feet
from the creek. You and your friend walk away from each other in opposite parallel directions. Your friend
walks 50 feet and you walk 12 feet.
1. Label and angle relationships that you
know on the diagram. Explain how you
know these angle measures.
2. How do you know that they triangle formed by the lines are similar?
3. Calculate the distance from your friend’s starting point to your side of the creek. Round your answer
to the nearest tenth, if necessary.
4. What is the width of the creek?
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Secondary 2
Chapter 3/4
Additional Notes
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