Quantitative Aptitude Ques 2115

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 from the point S are drawn which touch the circle at P and Q. If $ \angle PSQ=20{}^\circ , $ then $ \angle PRQ $ is equal to

Options:

A) $ 200{}^\circ $

B) $ 160{}^\circ $

C) $ 100{}^\circ $

D) $ 80{}^\circ $

Show Answer

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 quadrilateral POQS,
    $ \angle PSQ=20{}^\circ $

$ \Rightarrow $ $ \angle OPS=\angle OQS=90{}^\circ $

$ \therefore $ $ \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.

$ \therefore $ $ \angle PRQ=180{}^\circ -\angle PTQ $ $ =180{}^\circ -80{}^\circ =100{}^\circ $