An acute triangle has to have three acute angles. An acute angle is less than 90˚.

An obtuse triangle has at least one angle larger than 90˚. An obtuse angle is less than 180˚ and more than 90˚.

Lastly a right triangle has one 90˚ angle.

Now, let’s talk about sides.

The first one that you need to know about is isosceles. An isosceles triangle is a triangle that has two sides that are the same length and one that is not the same length as the other two sides.

The second one that you need to know is an equilateral triangle and an equilateral triangle is when all three of the sides are the same.

Then the last one that you need to know is a scalene triangle and a scalene triangle is a triangle when none of the sides are the same.

## How to classify triangles by sides and angles

## Angles

Now, let’s talk about sides.