Download Isosceles and Equilateral Triangles

Isosceles and Equilateral
Triangles
1
Parts of an Isosceles Triangle


An isosceles triangle is a triangle with two congruent sides.
The congruent sides are called legs and the third side is called the base.
3
Ð 1 and Ð2 are base angles
Ð 3 is the vertex angle
Leg
Leg
1
2
Base
2
Isosceles Triangle Theorems
If two sides of a triangle are congruent, then the angles opposite those
sides are congruent.
A
If AB  AC , then B  C.
B
C
Example:
Find the value of x.
50 °
x°
Isosceles Triangle Theorems
If two angles of a triangle are congruent, then the sides opposite those
angles are congruent.
A
If B  C , then AB  AC.
B
Example:
Find the value of x.
A
3x - 7
B
x+15
50 °
50 °
C
C
Equilateral Triangles
Equilateral:
A triangle in which all 3 sides are equal.
G
GI = 3.70cm
GH = 3.7 cm
H
HI = 3.7 cm
I
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Equilateral Triangle Theorems
• If a triangle is equilateral, then it is equiangular.
• If a triangle is equiangular, then it is equilateral.
T
15 in.
S
What is the length of each side and angle?
R