Which one of the following equals for all real ?

MATHEMATICS · Single correct · CBSE · Mathematics · Trigonometric Functions · Trigonometric Functions

Problem

Which one of the following equals cos⁡2θ\cos 2\theta for all real θ\theta? (a) 2sin⁡θcos⁡θ2\sin\theta\cos\theta (b) 1−2cos⁡2θ1-2\cos^2\theta (c) cos⁡2θ−sin⁡2θ\cos^2\theta-\sin^2\theta (d) sin⁡2θ−cos⁡2θ\sin^2\theta-\cos^2\theta

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