Everyone learns the number one rule about triangles in high school: the angles of a triangle add up to 180 degrees. But did you know that sometimes they don't? Triangles are much more interesting ...

Learn about angles in triangles and quadrilaterals with this BBC Bitesize Maths article. For students between the ages of 11 and 14.

Calculating an angle The three trigonometric ratios can be used to calculate the size of an angle in a right-angled triangle.