Types of Triangles

Triangles have special names based on their side lengths and angle measures.

When you classify triangles by their side lengths, you use the words equilateral, isosceles, and scalene.

An equilateral triangle has three equal sides.

This is an example of a equilateral triangle.

An isosceles triangle has two equal sides.

This is an example of an isosceles triangle.

A scalene triangle has no equal sides.

This is an example of scalene triangle.

When you classify triangles by their angle measures, you use the words acute, right, and obtuse.

Let's find out what those words mean!

An acute triangle has three acute angles.

Acute angles measure less than 90°

This is an example of an acute triangle.

A right triangle has one angle.

Right angles measure exactly 90°.

This is an example of a right triangle.

Notice that all of the angles add up to be 180 degrees.

The angles in a triangle always add up to 180 degrees

An obtuse triangle has one obtuse angle.

Obtuse angles measure more than 90°.

This is an example of an obtuse triangle.

This is a right isosceles triangle.

It has a right angle and two equal sides.