If cos⁡θ=12x+1x then 12x2+1x2 is equal to

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sin 2θ

cos 2θ

tan 2θ

None of these

answer is B.

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Detailed Solution

Given that, cos⁡θ=12x+1x⇒x+1x=2cos⁡θ----iWe know that,x2+1x2=x+1x2−2=(2cos⁡θ)2−2=4cos2⁡θ−2=2cos⁡2θ∴12x2+1x2=12×2cos⁡2θ=cos⁡2θ

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