# Triangles

A triangle has three sides and is made of straight lines. A triangle may be classified by how many of its sides are of equal length. Or, it may be classified by what kind of angles it has.

### Types of Triangles by Length

In an **equilateral triangle,** all three sides are the same length. An equilateral triangle is always equiangular *(see below)*.

In an **isosceles triangle,** two sides are the same length. An isosceles triangle may be right, obtuse, or acute *(see below)*.

In a **scalene triangle,** none of the sides are the same length. A scalene triangle may be right, obtuse, or acute *(see below)*.

### Types of Triangle by Angle

In an **equiangular triangle,** all the angles are equal—each one measures 60 degrees. An equiangular triangle is a kind of acute triangle, and is always equilateral.

In a **right triangle,** one of the angles is a right angle—an angle of 90 degrees. A right triangle may be isosceles or scalene.

In an **obtuse triangle,** one angle is greater than a right angle—it is more than 90 degrees. An obtuse triangle may be isosceles or scalene.

In an **acute triangle,** all angles are less than right angles—each one is less than 90 degrees. An acute triangle may be equilateral, isosceles, or scalene.

**See also:**