The angles in a **triangle** add up to \({180}^\circ\).

The properties of different kinds of triangles are listed below.

- all sides are of equal length
- all angles are equal (\({60}^\circ\))

- two sides are of equal length
- two angles are equal (called the base angles)

- the three sides are all different lengths
- none of the angles are equal

- contains a right angle
- can be either isosceles or scalene

- all three angles are acute
- can be equilateral, isosceles or scalene

- contains an obtuse angle
- can be either isosceles or scalene

Within all triangles, the longest side is opposite the largest angle, and the shortest side is opposite the smallest angle. If two, or three, angles are the same size, then the sides opposite are of equal length.