# Properties of triangles

The angles in a triangle add up to $${180}^\circ$$.

The properties of different kinds of triangles are listed below.

## Equilateral triangle

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

## Isosceles triangle

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

## Scalene triangle

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

## Right-angled triangle

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

## Acute-angled triangle

• all three angles are
• can be equilateral, isosceles or scalene

## Obtuse-angled triangle

• contains an
• 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.