Solution: All 4 vertices touch the circumference of the circle. Using theorem 4. Opposite angles in a cyclic quadrilateral add up to 180° a = 180 – 60 = 120° b = 180 – 140 = 40° ...

Module 1 (M1) - Geometry & measures - Properties of angles Circle theorems are properties that are true for all circles, regardless of their size. There are six theorems to learn and recognise.