Which of the following identities is true for every acute angle ?

MATHEMATICS · Single correct · A Level · Mathematics · Trigonometry · Trigonometry

Problem

Which of the following identities is true for every acute angle θ\theta? (a) sin⁡2θ−cos⁡2θ=1\sin^2\theta-\cos^2\theta=1 (b) sin⁡θ+cos⁡θ=1\sin\theta+\cos\theta=1 (c) sin⁡2θ+cos⁡2θ=1\sin^2\theta+\cos^2\theta=1 (d) sin⁡2θ+tan⁡2θ=1\sin^2\theta+\tan^2\theta=1

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