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4-8. Isosceles and Equilateral Triangles. Warm Up. Lesson Presentation. Lesson Quiz. Holt Geometry. Do Now 1. Find each angle measure. True or False. If false explain. 2. Every equilateral triangle is isosceles. 3. Every isosceles triangle is equilateral. Objective.

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4-8

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  1. 4-8 Isosceles and Equilateral Triangles Warm Up Lesson Presentation Lesson Quiz Holt Geometry

  2. Do Now • 1. Find each angle measure. • True or False. If false explain. • 2. Every equilateral triangle is isosceles. • 3. Every isosceles triangle is equilateral.

  3. Objective Apply properties of isosceles and equilateral triangles.

  4. Vocabulary legs of an isosceles triangle vertex angle base base angles

  5. In an Isosceles triangle, the congruent sides are called the legs. The vertex angle is the angle formed by the legs. The side opposite the vertex angle is called the base, and the base angles are the two angles that have the base as a side. 3 is the vertex angle. 1 and 2 are the base angles.

  6. Reading Math The Isosceles Triangle Theorem is sometimes stated as “Base angles of an isosceles triangle are congruent.”

  7. The length of YX is 20 feet. Explain why the length of YZ is the same. Example 1: Astronomy Application

  8. Example 2: Finding the Measure of an Angle Find mF.

  9. Example 3: Finding the Measure of an Angle Find mG.

  10. Example 4 Find mH.

  11. Example 5 Find mN.

  12. The following corollary and its converse show the connection between equilateral triangles and equiangular triangles.

  13. Example 6: Using Properties of Equilateral Triangles Find the value of x.

  14. Example 7: Using Properties of Equilateral Triangles Find the value of y.

  15. Example 8 Find the value of JL.

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

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