2. Isosceles Triangles

4. Definitions - Review ABC is an isosceles triangle. Name each item(s): Vertex Angle Base Legs Base Angles AC AB, CB Side opposite C AB Angle opposite BC

5. A C B A B C A C B Yes Yes No

6. Isosceles Triangle Theorem If two sides of a triangle are congruent, then the angles opposite those sides are congruent.

7. Example 1 Find the measure of each angle. x + x + 30 o = 180 o 2x + 30 o = 180 o 2x = 150 o x = 75 o

8. Example 2 Find the length of each side. 3x – 6 2x 6 3x – 6 = 6 3x = 12 x = 4 EF = 6 EG = 8

9. Example 3 Find the measure of each angle. (2x – 4) + (x + 2) + (x + 2) = 180 o 4x = 180 o x = 45 o

11. Practice - What do we still need to know to prove the triangles are congruent? C A B M N F P

14. 2x 2x x 62