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Question Number 115248 by aye48 last updated on 24/Sep/20

$$\mathrm{Express}\cos 4\mathrm{x}\mathrm{interm}\mathrm{of}\cos \mathrm{x}.$$

Answered by Olaf last updated on 24/Sep/20

$$\cos 4x={2\cos }^{2}2x-1$$$$\cos 4x=2{({2\cos }^{2}x-1)}^2-1$$$$\cos 4x=2({4\cos }^{4}x-{4\cos }^{2}x+1)-1$$$$\cos 4x={8\cos }^{4}x-{8\cos }^{2}x+1$$$$$$

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