Question: P and Q are two points on a circle with centre at O. R is a point on the minor arc of the circle between the points P and Q. The tangents to the circle at the points P and Q meet each other at the point S. If $ \angle PSQ=20{}^\circ , $ then $ \angle PRQ $ is equal to
Options:
A) $ 200{}^\circ $
B) $ 160{}^\circ $
C) $ 100{}^\circ $
D) $ 80{}^\circ $
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Answer:
Correct Answer: C
Solution:
- Join P and Q with an another point, say T, on the major arc.
Also, join PO and QO.
In POQS, $ \angle PSQ=20{}^\circ $
$ \angle OPS=\angle OQS=90{}^\circ $ [ $ \because $ Tangent]
$ \angle POQ=360{}^\circ -(90{}^\circ +90{}^\circ +20{}^\circ )=160{}^\circ $
$ \therefore $ $ \angle PTQ=\frac{1}{2}\angle POQ=\frac{1}{2}\times 160{}^\circ =80{}^\circ $
Now, PTQR is a cyclic quadrilateral.
$ \angle PRQ=180{}^\circ -\angle PTQ $
$ =180{}^\circ -80{}^\circ =100{}^\circ $