Isosceles and Equilateral Triangles

Section 5.4

Triangles

• Opposite – Across from

A

B

C

Example

Side opposite A is BC

Angle opposite AB is C

Isosceles Triangle Anatomy

LegLeg

Base

Base Angles

Vertex Angle

Base Angles Theorem

• If two sides of a triangle are congruent, then the angles opposite them are congruent.

402 x 223 x

Converse of Base Angles Theorem• The converse is also true!

63 x

10x

Example

NL SL

Name what sides or angles must be congruent with the given information.

1 4M

N

L

R

T

S

12

34

5

6

7

8

10

9

11

9 10

Corollary to Base Angles Thm.

• If a triangle is equilateral, then the triangle is equiangular.

• The converse of this statement is also true.

Example

Lesson 5.4 p.256; 3-16, 23-24, 42-44