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Question


If (1x2n)+(1y2n)=a(xnyn), then (1x2n1y2n)dydx is equal to


Options:
A .   xn1yn1
B .   yn1xn1
C .   xy
D .   1
Answer: Option A
:
A
Put xn=sin θ and yn=sin ϕthen,   (cosθ+cosϕ)=a(sinθsinϕ)2 cos(θ+ϕ2)cos(θϕ2)=2a cos(θ+ϕ2)sin(θϕ2)cot(θϕ2)=a(θϕ2)=cot1aθϕ=2cot1aor           sin1xnsin1yn=2 cot1aDifferentiating both sides,we havenxn1(1x2n)nyn1(1y2n)dydx=0           (1x2n1y2n)dydx=xn1yn1

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