The two tangents from an external point P to a circle with centre at O are PA and PB. If ∠APB=70°, then the value of ∠ AOB is:(2 mark)
∠ OAP = 90°
∠ APO = 35°
(As, ∠ APB = 70°)
∠ AOP = 180° – (90° + 35°) (1 mark)
= 180° – 125° = 55°
∠ AOB = 2 x 55° = 110°(1 mark)