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α, β and y are the parametric angles of three points P, Q, and R respectively, on the circle x2 + y2 = 1, and A is the point (-1, 0). If the lengths of the chords AP, AQ and AR are in GP, then cos α/2, cos β/2 and cos γ/2 are in

a
AP
b
GP
c
HP
d
none of these

detailed solution

Correct option is B

Let P (cos α, sinα), Q (cos β, sin β) and R (cosγ, sin γ) be three specified points on the given circle. Then,              AP=(−1−cos⁡α)2+(0−sin⁡α)2⇒ AP=2+2cos⁡α=4cos2⁡α/2=2cos⁡α/2Similarly, we have     AQ=2cos⁡β/2 and AR=2cos⁡γ/2Now,      AP, AQ, AR are in GP⇒ 2cos⁡α/2,2cos⁡β/2,2cos⁡γ/2 are in GP⇒ cos⁡α/2,cos⁡β/2,cos⁡γ/2 are in GP.

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