Problem

Problem

If cos⁡−1x=cos⁡−1y2=α\cos^{-1} x = \cos^{-1} \frac{y}{2} = \alpha , then 4x2−4xycos⁡α+y24x^2 - 4xy \cos \alpha + y^2 equal to a. −4sin⁡2α-4 \sin^2 \alpha b. 4sin⁡2α4 \sin^2 \alpha c. 4 d. 2sin⁡2α2 \sin 2\alpha

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