Learn about and revise angles, lines and multi-sided shapes and their properties with this BBC Bitesize GCSE Maths Edexcel study guide.

A right-angled triangle is a triangle that has a right angle. Labelling angles and sides. ... The interior angle and its corresponding exterior angle always add up to 180°.

For example, the sum of the angles of the triangles on the Poincare disk below is 30 degrees + 90 degrees + 45 degrees = 165 degrees. The sides of these triangles do not look straight, ...