Prior knowledge you need to have in order to work out the size of unknown angles in triangles are:

  • Angles on straight lines add up to 180°
  • Angles around a point add up to 360°
  • When two straight lines cross the opposite angles are equal

This video starts by looking at the properties of the different types of triangles like namely scalene, isosceles, equilateral and right-angled triangle. It then covers the following angle properties:

  • Interior angles of a triangle adds up to 180°
  • Exterior angles of a triangle equals the sum of the opposite interior angles