# Triangles

**Naming triangles**

There are three types of triangles:

Equilateral triangle – all sides and angles are equal

Isosceles triangle – two sides and angles are equal

Scalene triangle – none of the sides or angles are equal

Triangles can also be named according to their angles:

Right angled triangle – contains a right angle

Acute angled triangle – contains acute angles

Obtuse angled triangle – contains an obtuse angles

**Angles in a triangle**

All angles in a triangle add up to 180°.

Any exterior angle in a triangle is equal to the sum of the two opposite interior angles.