1. 7.2 Similar Polygons Two polygons are similar (~) if and only if their
Corresponding angles are 
and the measures of the corresponding sides are proportional.
Same shape but not necessarily the same size.

2. Small ~ Large Find x & y. 3 8 8x = 24 Cross Multiply 4
x = Divide by 8 – Solve for x. y x 6
8y = Cross Multiply
y = Divide by 8 – solve for x.

3. Scale Factor
When you compare the lengths of corresponding sides of similar figures, you usually get a numerical ratio. This ratio is called the scale factor for the two figures.
The height of the Soldiers’ National Monument in Gettysburg, Pennsylvania is 60 feet. The height of a model is 10 inches. What is the scale factor of the model compared to the original?
1st: Convert 60 feet to inches: 60(12) = 720 inches
2nd: Write a proportion and simplify

4. Proportional Parts and Scale Factor
Write a similarity statement, then find a and the scale factor of the big triangle to the small triangle. K L J X Y Z
a in
3 in
2 in
1.5 in
Similarity Statement (match up the vertices):
Scale Factor: 3/2

5. Textbook Example
Problem similar to p Example #5

6. Homework
#46 p , odd, even, 48, 57-58