1. Collect any late or redone homework
(in your HW notebook)
Dec. 6, 2012
Title: Activity Lab 5-5a (p. 251)
Exploring Similar Figures
Pre-Activity Questions:
What makes two shapes similar?
Are all triangles similar?

2. Activity Lab 5-5a on page 251
You’ll need your protractor and a pencil.
How will you be graded on this?
- on-task
- helping others (bonus!)
- neatly done
- accurately done
- How clearly did you answer question 4?

3. Two polygons are similar if Corresponding angles are equal; AND
Using Similar Figures
LESSON 5-5
Concept summary
Two polygons are similar if
Corresponding angles are equal; AND
Lengths of corresponding sides form equivalent ratios
5-5

4. ABC is similar to DEF. Find the value of c.
Using Similar Figures
LESSON 5-5
Additional Examples
ABC is similar to DEF. Find the value of c. = c 18 6 9
Write a proportion.
Write the cross products.
9c = 18 • 6
Divide each side by 9. 9c 9
108 =
Solve for c.
c = 12
Quick Check
5-5

5. Write the cross products. 12x = 5 • 42
Using Similar Figures
LESSON 5-5
Additional Examples
A 5-ft person near a tree has a shadow 12 ft long. The tree has a shadow 42 ft long. What is the height of the tree?
Draw a diagram like the one at the right. Let x represent the height of the tree. = x 5 42 12
Write a proportion.
Write the cross products.
12x = 5 • 42
Divide each side by 12.
12x 12
5 • 42 =
Simplify.
x = 17 1 2
The height of the tree is ft. 1 2
Quick Check
5-5

6. Using Similar Figures
LESSON 5-5
Closure
Q1) Angle measures of a triangle are 40, 60 and 80 degrees. Angle measures of a similar triangle will be?
Q2) Side lengths of a triangle are 40 cm, 60 cm and 80 cm. Smallest length of a similar triangle is 120 cm. What are the lengths of the other two sides?
5-5

7. The angle measures would also be 40, 60, and 80 degrees.
Using Similar Figures
LESSON 5-5
Closure
Q1) Angle measures of a triangle are 40, 60 and 80 degrees. Angle measures of a similar triangle will be?
The angle measures would also be 40, 60, and 80 degrees.
Q2) Side lengths of a triangle are 40 cm, 60 cm and 80 cm. Smallest length of a similar triangle is 120 cm. What are the lengths of the other two sides?
The lengths of the other two sides are 180 cm and 240 cm.
5-5

8. In the figure below, JKL ~ XYZ.
Using Similar Figures
LESSON 5-5
Lesson Quiz – Write this in your Notes notebook
In the figure below, JKL ~ XYZ.
1. Which angle besides K has measure 29°?
2. Find YZ.
3. A 4-ft-tall person standing near a telephone pole has a shadow 3 ft long. At the same time, the telephone pole has a shadow 18 ft long. What is the height of the telephone pole? Y 9
24 ft
5-5

9. Wednesday: Similar Figures and Indirect Measurement (handout)
HOMEWORK
Wednesday: Similar Figures and Indirect Measurement (handout)
Thurs: Scale Model Project due (with rubric and calculations)
5-5