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Question
The tangent to the curve x =  acos2θcosθ,y=acos2θsinθ at the point corresponding to θ=π6 is
Options:
A .  parallel to the x-axis
B .  parallel to the y-axis
C .  parallel to line y = x    
D .  3X-4Y+2=0
Answer: Option A
:
A
dxdθ=acos2θsinθ+acosθsinθcos2θ=a(cos2θsinθ+cosθsin2θ)cos2θ=asin3θcos2θ=dydθ=acos2θcosθasinθsin2θcos2θ=acos3θcos2θ
Hence dydx=cot3θdydx|θ=π6 = 0
So the tangent to the curve at θ=π6 is parallel to the x-axis.

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