1 10/16/12 Triangles Unit Similar Polygons

2 Definition:Two polygons are similar if: 1. Corresponding angles are congruent. 2. Corresponding sides are in the same ratio. The scale factor is the ratio between a pair of corresponding sides. Scale Factor: Two polygons are similar if they have the same shape not necessarily have the same size.

3 Naming Similar Polygons When naming similar polygons, the vertices (angles, sides) must be named in the corresponding order. AB CD PQ R S

4 Example- The two polygons are similar. Solve for x, y and z. Step 3: Find the scale factor between the two polygons. Note: The scale factor has the larger quadrilateral in the numerator and the smaller quadrilateral in the denominator. Step1: Write the proportion of the sides. Step 2: Replace the proportion with values. Step 4: Write separate proportions for each missing side and solve. 5 z x 10 y B C A D F G E H

5 Scale factor is same as the ratio of the sides. Always put the first polygon mentioned in the numerator. Example: What is the scale factor from  ZYX to  ABC? The scale factor from  ABC to  ZYX is 2/1. If  ABC ~  ZYX, find the scale factor from  ABC to  ZYX C A B Z Y X ½