# What are the different types of triangles?

A triangle is a three-sided plane figure with three sides and three angles.

The sum of the three angles always equals 180 degrees.

Up first are triangles that are classified by the length of their sides.

A Scalene triangle has three different side lengths.

An isosceles triangle has two congruent or equal sides, and an Equilateral triangle has three congruent or equal sides.

### Triangles can also be classified by their angles.

There are three angles often associated with triangles.

• Acute angles are less than 90 degrees

• Right angles are exactly 90 degrees

• Obtuse angles are greater than 90 degrees

All triangles have two acute angles and the third angle determines the type of

the triangle you have.

An acute triangle is a triangle with three angles that measure less than 90 degrees

An obtuse triangle is a triangle with one angle greater than 90 degrees.

A right triangle is a triangle with one right angle or ( 90 degrees).

Triangles are also classified by side length and angle measure.

This chart summarizes triangles classified by side length and angle measure.

A scalene triangle, remember it has three different side lengths can be acute…. right…. and an obtuse triangle.

An isosceles triangle, remember 2 equal sides, can also be acute…., right…., and obtuse triangle.

An equilateral triangle can only be acute because in order to have three sides that are equal the angle measure must be 60 degrees.

Why interior angles triangle = 180 degrees