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Question Number 148445 by mathdanisur last updated on 28/Jul/21

$$ifcos\mathit{\alpha }=\sqrt{\mathit{a}}$$$$find5-6cos2\mathit{\alpha }+cos4\mathit{\alpha }=?$$

Commented by mathdanisur last updated on 28/Jul/21

$$ThankyouSer$$$$But,=\sqrt{\mathit{\alpha }}\left(alfano\right)=\sqrt{\mathit{a}}$$

Commented by mathdanisur last updated on 28/Jul/21

$$answer:a)8a^2-20a+12b)8a^2+18a-12$$$$c)2a-1d)8a^2-8a+1e)1-5a$$

Commented by Olaf_Thorendsen last updated on 28/Jul/21

$$\mathrm{you}\mathrm{are}\mathrm{right}!$$$$\mathrm{sorry}\mathrm{mister}.$$$$\mathrm{my}\mathrm{eyes}\mathrm{are}\mathrm{very}\mathrm{old}.$$

Answered by Olaf_Thorendsen last updated on 28/Jul/21

$$x=5-6\cos 2\alpha +\cos 4\alpha$$$$x=5-6\cos 2\alpha +{2\cos }^{2}2\alpha -1$$$$x={2\cos }^{2}2\alpha -6\cos 2\alpha +4$$$$x=2{({2\cos }^2\alpha -1)}^2-6({2\cos }^2\alpha -1)+4$$$$x=2{(2a-1)}^2-6(2a-1)+4$$$$x=8a^2-20a+12$$

Commented by mathdanisur last updated on 28/Jul/21

$$ThankyouverymuchSir$$

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