In the diagram, POQ is the diameter of the circle centre O. Calculate ∠QRS
A.
35o
B.
70o
C.
100o
D.
125o
Correct answer is A
∠PSQ = 90° (angle in a semi-circle)
(when SR is joined to SP)
∠SPQ = 180 – (90+35) = 180 – 125 = 55°
∠QRS + ∠SPQ = 180° (opposite angles in a cyclic quad is supplementary)
∠QRS = 180° - 55°
= 125°