Warm Up 1. Find each angle measure. True or False. If false explain.

1. 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. 60°; 60°; 60° True False; an isosceles triangle can have only two congruent sides.

2. Notes 4-6 Isosceles Triangles

3. Isosceles Triangles • Isosceles triangle – at least two congruent sides. • Congruent sides – legs. • Vertex angle – angle formed by the legs. • Side opposite the vertex angle is the base. • Base angles – the two angles that have the base as a side. 3 is the vertex angle. 1 and 2 are the base angles.

5. Example: Finding the Measure of an Angle Find mF. Thus mF = 79°

6. Example: Finding the Measure of an Angle Find mG. x= 22 Thus mG = 22° + 44° = 66°.

7. Example: Find mH. Thus mH = 66°

8. Example: Find mN. Thus mN = 6(8) =48°.

9. Example: Using Properties of Equilateral Triangles Find the value of x. ∆LKM is equilateral.

10. Example: Using Properties of Equilateral Triangles Find the value of y. ∆NPO is equiangular.

11. Lesson Quiz Find each angle measure. 1. mR 2. mP Find each value. 3.x 4.y 5.x 28° 124° 6 20 26°

12. Lesson Quiz 6. The vertex angle of an isosceles triangle measures (a + 15)°, and one of the base angles measures 7a°. Find a and each angle measure. a = 11; 26°; 77°; 77°