Find angles in a right angle

A right angle is exactly 90°. It is shown by a small square.

Right angle diagram

Angles that add together to make a right angle are called complementary angles.

If you know one complementary angle you can subtract it from 90° to find a missing angle.

Question

Calculate angle c.

90 degree angle, split into 20 degrees and unknown angle, c

A right angle is shown, so the two angles add up to 90°.

c = 90° - 20°

c = 70°

curriculum-key-fact
  • Complementary angles make a Corner (a right angle).