1. Warm Up
Explain what information you would need to prove two triangles congruent. Draw an example to help guide your response.
I will be asking for people to share their responses! (and I will be collecting this).

2. 4.6 Isosceles and Equilateral Triangles

3. Isosceles Triangle Properties
The two congruent sides are called the legs of an isosceles triangle, and the angle with the sides that are the legs is called the vertex angle. The side of the triangle opposite the vertex angle is called the base. The two angles formed by the base and the congruent sides are called the base angles.
Ð1 is the vertex angle.
Ð2 and Ð3 are the
base angles.

4. Isosceles Triangle Theorems

5. Example 1 a) Name two unmarked congruent angles.
b) Name two unmarked congruent segments.

6. Example 1 Continued
c) Which statement correctly names two congruent angles?
a) ÐPMJ
b) ÐJKM
c) ÐJKP 
d) ÐPLK

7. Equilateral Triangle Corollaries
The Isosceles Triangle Theorem leads to two corollaries about the angles of an equilateral triangle.

8. Example 2
a) Find mÐR
b) Find PR.

9. Example 3
You can use the properties of equilateral triangles and algebra to find missing values.
Find the value of each variable.

10. Example 4

11. Exit Slip