Lesson 3-2 Isosceles Triangles.

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Presentation transcript:

Lesson 3-2 Isosceles Triangles

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.

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

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