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Question Number 159787 by abdullah_ff last updated on 21/Nov/21

$$\mathrm{if}{cos}^4\theta -{sin}^4\theta =2-5cos\theta$$$$\mathrm{then}\mathrm{find}\mathrm{the}\mathrm{value}\mathrm{of}\theta$$

Commented by cortano last updated on 21/Nov/21

$$\Rightarrow \cos {}^2\theta -\sin {}^2\theta -2+5\cos \theta =0$$$$\Rightarrow \cos {}^2\theta -1+\cos {}^2\theta -2+5\cos \theta =0$$$$\Rightarrow 2\cos {}^2\theta +5\cos \theta -3=0$$$$\Rightarrow (2\cos \theta -1)(\cos \theta +3)=0$$$$\Rightarrow \cos \theta =\frac{1}{2}\Rightarrow \theta =\pm \frac{\pi }{3}+2n\pi$$

Commented by abdullah_ff last updated on 23/Nov/21

$$thankyousir$$

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