﻿ Triangle Types and Classifications: Isosceles, Equilateral, Obtuse, Acute and Scalene

# 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

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

Each angle is 60°.

#### Isosceles triangle

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

#### Scalene Triangle

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

#### Acute Triangle

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

#### Obtuse Triangle

The Obtuse Triangle has an obtuse angle (an obtuse angle has more than 90°). In the picture on the left, the shaded angle is the obtuse angle that distinguishes this triangle.

Since the total degrees in any triangle is 180°, an obtuse triangle can only have one angle that measures more than 90°.

### Practice Problems

##### Practice 4

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

##### Practice 4

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