Download Isosceles Triangle

Lesson 4-5: Isosceles &
Equilateral Triangles
Vocab
Legs
The congruent sides of an isosceles ∆
Base Angles
Congruent angles opposite the legs of an isosceles ∆
Equiangular
A triangle with all three angles congruent (all 600)
– also equilateral
Bisects
Cuts into 2 equal pieces
Isosceles Triangle
leg
leg
Always start by
identifying base
angles and legs!
base
base angles
•Legs are congruent
•Base angles are congruent
If one is true, the
other must be true!
•If we know 1 angle, we can find the rest
Multiple-Choice Test Item
If
and
measure of
what is the
Mark given
information first
Identify legs &
base angles
Use angle
relationships
A. 25
Answer: A
B. 35
C. 50
D. 130
Equilateral Triangles
•A special type of isosceles triangle
•All sides and angles are congruent
•Also called equiangular
•All angles must be 600
ABC is an equilateral triangle.
a. Find x.
Answer: 30
b.
Answer: 90
bisects