Page 94 - Math Course 3 (Book 2)

Properties of Isosceles and Equilateral Triangles
Mo. 9

Lesson 6

KEY CONCEPTS:

1. Use properties of isosceles triangles.
2. Find the congruent segments and angles
of isosceles triangles.
3. Use properties of equilateral triangles.

MO. 9 - L6a THEOREM 9.5

Properties of Isosceles Isosceles Triangle
Triangles If two sides of a triangle are congruent, then the

angles opposite those sides are congruent.

Vocabulary A-Z Example: If AB ≅ CB, then ∠A ≅ ∠C.

Let us learn some vocabulary C

vertex angle
The angle formed by the congruent sides is called A B
the vertex angle.

Vertex angle
THEOREM 9.6
leg
Isosceles Triangle
If two angles of a triangle are congruent, then the
sides opposite those angles are congruent.
base
Abbreviation: Conv. of Isos. △ Th.
base angles Example: If ∠D ≅ ∠F, then DE ≅ FE.
The two angles formed by the base and one of the
congruent sides are called base angles. D

leg E

Base angle
F
base

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