Types of Triangles

Isosceles, Equilateral, Scalene, Obtuse...

Triangles can be classified by various properties relating to their angles and sides. The most common classifications are described on this page.

Classifications of Triangles

Equilateral triangle

picture of equilateral triangle

The Equilateral triangleshown on the left has three congruent sides and three congruent angles.

Each angle is 60°.

Isosceles triangle

Isosceles Triangle

The Isosceles triangle shown on the left has two equal sides and two equal angles.

Scalene Triangle

Scalene Triangle

The Scalene Triangle has no congruent sides. In other words, each side must have a different length.

Acute Triangle

Acute Triangle

The Acute Triangle has three acute angles (an acute angle measures less than 90°).

Practice Problems

Practice 4

Classify the triangle on the left.

Obtuse

Assuming the picture is to scale, the triangle on the right is definitely obtuse (see the blue angle) as well as scalene.

Practice 4

Classify the triangle on the left.

Obtuse

Assuming the picture is to scale, the triangle on the right is definitely acute as well as scalene.

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