cos 2(theta + phi ) - 4cos (theta + phi& | vedclass

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Question

(a) We have,$\cos 2(	heta + \phi ) - 4\cos (	heta + \phi )\sin 	heta \sin \phi + 2{\sin ^2}\phi  $

Now, put $	heta = \phi&n

Vedclass · Accepted Answer

$\cos 2	heta $

Vedclass · Answer

(a) We have,$\cos 2(	heta + \phi ) - 4\cos (	heta + \phi )\sin 	heta \sin \phi + 2{\sin ^2}\phi  $

Now, put $	heta = \phi = \frac{\pi }{4}$

$\cos 2\left( {\frac{\pi }{2}} ight) - 4\cos \left( {\frac{\pi }{2}} ight)\sin \left( {\frac{\pi }{4}} ight)\sin \left( {\frac{\pi }{4}} ight) + 2{\sin ^2}\left( {\frac{{2\pi }}{4}} ight) = 0$

Put $	heta = \phi = \pi /4$  in option $(a)$, 

then, $\cos 2	heta = \cos \pi /2 = 0$.

Hence option $(a)$ is correct.

$\cos 2(\theta + \phi ) - 4\cos (\theta + \phi )\sin \theta \sin \phi + 2{\sin ^2}\phi = $

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