1. Geometry Sources: Discovering Geometry (2008) by Michael Serra Geometry (2007) by Ron Larson

2.  We define similar triangles in Geometry as triangles having the same shape; specifically having congruent corresponding angles and proportional corresponding sides.

3. 15 21 18 Are the two triangles similar? 5 7 6 Yes they are! Scale factor is 3! Because the triangles are similar, the corresponding angles are congruent!

4.  If two angles of a triangle are congruent to two angles of another triangle, then the two triangles are similar. AA Similarity Postulate

5. Are the two triangles similar ?

7.  If the ratios of the 3 pairs of corresponding sides of two triangles are equal, then the two triangles are similar. SSS Similarity Conjecture

8. Are the two triangles similar ? All 3 pairs of sides have equal ratios! Therefore the two triangles are similar!

9. Are the two triangles similar ? All 3 pairs of sides have equal ratios! Therefore the two triangles are similar!

10.  If the ratios of 2 pairs of corresponding sides of two triangles are equal, and the included angles are congruent, then the two triangles are similar. SAS Similarity Conjecture

11. Are the two triangles similar ? Yes they are similar by SAS Similarity Conj.