4-8 Isosceles and Equilateral Triangles

4-8 Isosceles and Equilateral
Triangles
Learning Objective: Students will be able to apply
properties of isosceles and equilateral triangles.
February 11, 2013

Ex 1: Isosceles Triangles
• Vertex angle- the angle formed by the legs
• Base angles- the two angles that have the base as a side
• 4-8-1 Isosceles Triangle Theorem- If two sides of a
triangle are congruent, then the angles opposite the sides are
congruent.
• 4-8-2 Converse of the Isosceles Triangle Theorem- If
the two angles of a triangle are congruent, then the sides
opposite those angles are congruent.

Ex 2: Finding the Measure of an Angle
• Find each angle measure.
a)
b)
3x°
22°
(x + 44)°

Ex 3: Equilateral Triangles
• Corollary 4-8-3 Equilateral Triangle- If a triangle is
equilateral, then it is equiangular.
• Corollary 4-8-4 Equiangular Triangle- If a triangle is
equiangular, then it is equilateral.

Ex 4: Properties of Equilateral Triangles
• Find each value.
a)
(2x + 32)°
b)
5y – 6
4y + 12

Guided Practice
• Find each angle measure.
a)
48°
b)
6y°
(8y – 16)°

Assignment
Pg. 276 #3-10, 13-20
Show all work.