# Triangles: Classification

A triangle is a polygon with three sides.

Triangles can be classified by side length or by angle measure .

 Classification by Side Length Equilateral Triangle All sides congruent Isosceles Triangle At least two sides congruent Scalene Triangle No sides congruent

 Classification by Angle Measure Acute Triangle All interior angles measure less than $90°$ Right Triangle Exactly one interior angle measures $90°$ Obtuse Triangle Exactly one interior angle measures more than $90°$