If , then the value of…

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

Problem

If cos⁡2θ=(2+1)(cos⁡θ−12)\cos 2\theta=(\sqrt{2}+1)\left(\cos\theta-\frac{1}{\sqrt{2}}\right), then the value of θ\theta is (1) 2nπ+π42n\pi+\frac{\pi}{4} (2) 2nπ±π42n\pi\pm\frac{\pi}{4} (3) 2nπ−π42n\pi-\frac{\pi}{4} (4) None of these

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