Given and is acute with

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

Problem

Given sin⁡2θ=45\sin 2\theta = \dfrac{4}{5} and θ\theta is acute with sin⁡θ<cos⁡θ\sin \theta < \cos \theta, find cos⁡θ\cos \theta. (a) 15\dfrac{1}{\sqrt{5}} (b) 25\sqrt{\dfrac{2}{5}} (c) 25\dfrac{2}{\sqrt{5}} (d) 215\dfrac{\sqrt{21}}{5}

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