1. Lesson 3-2
Isosceles Triangles

2. Parts of An Isosceles Triangle
An isosceles triangle is a triangle with two congruent sides.
The congruent sides are called legs and the third side is called the base.

3. Isosceles Triangle Theorems
If two sides of a triangle are congruent, then the angles opposite those sides are congruent.
If two angles of a triangle are congruent, then the sides opposite those angles are congruent.
By the Isosceles Triangle Theorem,
the third angle must also be x.
Therefore,
x + x + 50 = 180
2x + 50 = 180
2x = 130
x = 65

4. More Examples Since two angles are congruent, the
sides opposite these angles must be
congruent.
3x – 7 = x + 15
2x = 22
X = 11