This document discusses properties of isosceles and equilateral triangles. It states that if two sides or two angles of a triangle are congruent, then the angles opposite the congruent sides or the sides opposite the congruent angles are also congruent. It also notes that a triangle is equilateral if and only if it is equiangular, and that each angle of an equilateral triangle measures 60 degrees. The document provides examples and problems involving isosceles triangles and outlines a lesson plan on isosceles triangles including essential questions, input, guided practice, and assessment.

1. Isosceles Triangles

2.  How can I use the properties of isosceles and
equilateral triangles?

3. Leg
Base
Vertex Angle
Base Angles

4.  Theorem 4.9
◦ If two sides of a triangle are congruent, then the
angles opposite those sides are congruent.
A
B
C

5.  Theorem 4.10
◦ If two angles of a triangle are congruent, then the
sides opposite those sides are congruent.
A
B
C

6.  Find x if CB AB

7. If DE CD, D
BC AC, and
m CDE 120, C
B
what is the measureof BAC?
E
A

9.  Corollary 4.3
◦ A triangle is equilateral if and only if it is
equiangular.
 Corollary 4.4
◦ Each angle of an equilateral triangle measures 60°.

10.  Find x

11.  Worksheet

12.  Intro- Isosceles triangles have special
properties.
 Standards- 4.4 (power)
 Supplies – slides, whiteboard
 Day 1:
◦ Essential Questions- slide 2
◦ Input-slides 3, 4, 5, and 9
◦ Guided Practice – slides 6, 7, 8, and 10
◦ Independent Practice – slide 11
 Assessment: Chapter Test