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Transcript 
4-8
Triangles
4-8 Isosceles
Isoscelesand
and Equilateral
Equilateral Triangles
Warm Up
Lesson Presentation
Lesson Quiz
Holt
Geometry
Holt
Geometry
4-8 Isosceles and Equilateral Triangles
Warm Up
1. Find each angle measure.
60°; 60°; 60°
True or False. If false explain.
2. Every equilateral triangle is isosceles.
True
3. Every isosceles triangle is equilateral.
False; an isosceles triangle can have
only two congruent sides.
Holt Geometry
4-8 Isosceles and Equilateral Triangles
Objectives
Prove theorems about isosceles and
equilateral triangles.
Apply properties of isosceles and
equilateral triangles.
Holt Geometry
4-8 Isosceles and Equilateral Triangles
Vocabulary
legs of an isosceles triangle
vertex angle
base
base angles
Holt Geometry
4-8 Isosceles and Equilateral Triangles
Note 48
Recall that an isosceles triangle has at least two
congruent sides. 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.
Holt Geometry
4-8 Isosceles and Equilateral Triangles
Holt Geometry
4-8 Isosceles and Equilateral Triangles
Example 1A: Finding the Measure of an Angle
Find mF.
Holt Geometry
4-8 Isosceles and Equilateral Triangles
Example 2B: Finding the Measure of an Angle
Find mG.
Holt Geometry
4-8 Isosceles and Equilateral Triangles
Check It Out! Example 2A
Find mH.
Holt Geometry
4-8 Isosceles and Equilateral Triangles
Check It Out! Example 2B
Find mN.
Holt Geometry
4-8 Isosceles and Equilateral Triangles
The following corollary and its converse show the
connection between equilateral triangles and
equiangular triangles.
Holt Geometry
4-8 Isosceles and Equilateral Triangles
Holt Geometry
4-8 Isosceles and Equilateral Triangles
Example 3A: Using Properties of Equilateral
Triangles
Find the value of x.
Holt Geometry
4-8 Isosceles and Equilateral Triangles
Example 3B: Using Properties of Equilateral
Triangles
Find the value of y.
Holt Geometry
4-8 Isosceles and Equilateral Triangles
Exit Slip
Find each angle measure.
1. mR
28°
124
2. mP
°
Find each value.
3. x
5. x
Holt Geometry
20
4. y
26°
6
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