~ Chapter 7 Section 3 Polygons are similar if: (Similar Polygons) Chapter 7 Section 3 (Similar Polygons) Polygons are similar if: 1. Corresponding angles are congruent 2. Corresponding sides are proportional Similar polygons have the same shape, but not necessarily the same size. ~ Similar polygons are denoted by:

ABCD & WXYZ are not drawn to scale! Given: B X A W C Y Z D ABCD & WXYZ are not drawn to scale!

B X A W C Y Z D

B X A W C Y Z D

B X A W C Y Z D

B X A W C Y Z D

B X A W C Y Z D

B X A W C Y Z D

B X A W C Y Z D

B X A W C Y Z D

B X A W C Y Z D

If polygons are similar, then… If polygons are similar, then… The longest side of one corresponds… …to the longest side of the other all the way down to the shortest sides.

Scale Factor: If ∆ABC ~ ∆ A’B’C’, then the scale factor is… the ratio of the lengths of any two corresponding sides must be simplified!!! B B’ 10 8 5 4 C C’ A A’ 3 6 If ∆ABC ~ ∆ A’B’C’, then the scale factor is…

Find: the measure of each angle, the measure of Given: Find: the measure of each angle, the measure of each side, and the scale factor A B 21 60° E F 100° 5 6 H G 12 D C 4

Are these polygons similar? 85º 105º

Consider the following… 1. If the corresponding angles of two polygons are congruent, must the polygons be similar? NO! 2. If the corresponding sides of two polygons are proportional, must the polygons be similar? NO! 3. If two polygons are congruent, must they be similar? YES! 4. Are all squares similar? YES!

Section 7.3 (p. 250-251) Written Exercises # 1 – 27 (all) Chapter 7 Section 3 (Similar Polygons) Homework: 7.2 Practice worksheet & Section 7.3 (p. 250-251) Written Exercises # 1 – 27 (all) For #1-14, if the answer is not always, then draw a picture showing why.