Mathematics

Mathematics

Problem

Which of the following equalities holds true for every real number xx? a) tan⁡2x+1=sec⁡x\tan^{2}x+1=\sec x b) sin⁡x+cos⁡x=1\sin x+\cos x=1 c) sin⁡2x+cos⁡2x=1\sin^{2}x+\cos^{2}x=1 d) sin⁡2x−cos⁡2x=1\sin^{2}x-\cos^{2}x=1

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