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Isosceles Triangle Theorem
See It in Action
Two examples of the idea done right—and one common look-alike that is not right.
EXAMPLE
EXAMPLE
NON-EXAMPLE
Definition
Isosceles Triangle Theorem: If two sides of a triangle are congruent, then the angles opposite those sides are congruent.
Key points:
Applies specifically to isosceles triangles (triangles with at least 2 congruent sides).
The congruent sides are called the legs; the third side is the base.
The angles opposite the legs are called the base angles, and they are congruent.
The converse is also true: If two angles of a triangle are congruent, then the sides opposite those angles are congruent.
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