1. Isosceles Triangles
Section 4.3

2. Warm Up
1. Find each angle measure.
True or False. If false explain.
2. Every equilateral triangle is isosceles.
3. Every isosceles triangle is equilateral.

3. Isosceles Triangle Theorem-If two sides of a triangle are congruent, then the angles opposite those sides are congruent.
Since , then:
The base is:
The vertex angle is:
The legs are:
The base angles are:
∠A is congruent to ∠C

4. Name the angles that must be congruent.

5. Find the value of x in each isosceles triangle.

6. If two angles of a triangle are congruent, then the sides opposite those angles are congruent.

7. Name the sides that must be congruent.

8. Find the value of x in each isosceles triangle.

9. 1. Find mF.

10. 2. Find mG.

11. 3. Find mH.

12. 4. Find mN.

13. 5. Find the value of x.

14. 6. Find the value of y.

15. 7. Find the value of JK.

16. 8. Find the value of y.

17. Find each angle measure. 1. mR 2. mP Find each value.
Lesson Quiz
Find each angle measure.
1. mR
2. mP
Find each value.
3. x
4. x