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Question

If θ=π2n+1, then cosθcos2θ2cos22θ...cos2n1θ=1an. Find a

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Solution

cosθcos2θcos22θ...cos2n1θ=1an
2n1(2sinθcosθ)cos2θcos22θ...cos2n1θ2nsinθ=2n2(2sin2θcos2θ)cos22θ...cos2n1θ2nsinθ=sin2nθ2nsinθ=1an
Substitute θ=π2n+1
sin2n(π2n+1)2nsin(π2n+1)=sin2n(ππ2n+1)2nsin(π2n+1)=12n=1an
Ans: 2

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