Which of the following is NOT an equivalent expression for ?

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

Problem

Which of the following is NOT an equivalent expression for cos⁡2θ\cos 2\theta? (a) cos⁡4θ−sin⁡4θ\cos^{4}\theta-\sin^{4}\theta (b) 1−2cos⁡2θ1-2\cos^{2}\theta (c) 1−tan⁡2θ1+tan⁡2θ\displaystyle\frac{1-\tan^{2}\theta}{1+\tan^{2}\theta} (d) cos⁡2θ−sin⁡2θ\cos^{2}\theta-\sin^{2}\theta

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