Section 4.4 – Using Triangle Congruence

Corresponding Parts of Congruent Triangles are Congruent (CPCTC)

When two triangles are proven congruent, then all other sides and angles are also congruent.

Flowchart Proof – visual proof where each statement is placed in a box and each reason is placed under the appropriate box.

Isosceles Triangle Theorem

- 2 sides congruent - legs are the 2 congruent - base is the remaining sides - base angles are the angles whose vertices are the endpoints of the base - vertex angle is the angle opposite the base

• If two sides of a triangle are congruent, then the angles opposite those sides are congruent (Base Angles are Congruent)
• If two angles of a triangle are congruent, then the sides opposite those angles are congruent (Base Angles are Congruent Converse)

corollary – an additional theorem that can easily be derived from the original theorem.

(a.k.a. “mini-theorem”

cor] The measure of each angle of an equilateral triangle is 60°.

cor] The bisector of the vertex angle of an isosceles triangle is the perpendicular bisector of the base.