4-5 Isosceles and Equilateral Triangles

Learning Goal 1. To use and apply properties of isosceles and equilateral triangles.

Vertex angle: The angle formed by the two congruent sides of an isosceles triangle. Base: Side opposite the vertex angle of an isosceles triangle. Legs: Congruent sides of an isosceles triangle.

Parts of an Isosceles Triangle Draw this big and label it with the definitions.

Vertex angle Base Leg Base angle Base angle

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

If ON = OJ, then J = N O J N ~~

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

If S = A, then SM = AM S A M ~~

Theorem 4-5 If a line bisects the vertex angle of an isosceles triangle, then the line is also the perpendicular bisector of the base.

Turn to page , 11-17, 25, 28, Points: 100% Complete 4 Points: 80% Complete 3 Points: 60% Complete 2 Points: 40% Complete 1 Point: 20% Complete