1. Date: Topic: Isosceles Triangle Theorem (6.1.C)
Warm-up
Given: S E O H R
Theorem: _______
SAS

2. Base angles of an isosceles triangle are congruent.
Isosceles Triangle Theorem: If two sides of a triangle are congruent, then the angles opposite those sides are congruent. This is sometimes stated:
Base angles of an isosceles triangle are congruent.
Find all the missing measures.
48˚
15 cm
15 cm
66˚
66˚
12.2 cm

3. Corollary 1
If a triangle is equilateral, then it is equiangular. B
Corollary
If a triangle is equiangular, then it is equilateral. A C
Find all the missing measures. 23
60˚
60˚
Corollary 2
The measure of each angle of an equilateral triangle is 60˚. 23 23
60˚

4. Z X Y 3x – 5 + 2x + 5 + 2x + 5 = 180 7x + 5 = 180 -5 -5 3(25)– 5 =
is an isosceles triangle. Find the missing information:
3x – 5 + 2x x + 5 = 180
7x + 5 = 180 Z
3(25)– 5 =
7x = 175
3x - 5
x = 25
2x + 5
2x + 5 X Y
2(25) + 5 =

5. C B A 7x - 4 = 3x + 32 180 – 59 – 59 = -3x +4 -3x +4 4x = 36 4 4 x = 9
is an isosceles triangle. Find the missing information:
7x - 4 = 3x + 32
180 – 59 – 59 =
-3x x +4 C
4x = 36
x = 9
7x - 4
3x + 32 B A
7(9) – 4 =
3(9) + 32 =