Question #0373f

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Answer 1 · 2017-03-11T07:12:32

$sin 2 x sin x - cos 2 x cos x = - cos x$ $sin 2x sin x - cos 2x cos x =-cos x$

$\Rightarrow cos 2 x cos x - sin 2 x sin x = cos x$ $=>cos 2x cos x-sin 2x sin x =cos x$

$\Rightarrow cos (2 x + x) = cos x$ $=>cos (2x + x) =cos x$

$\Rightarrow cos (3 x) = cos x$ $=>cos (3x) =cos x$

$=>3x=2npipmx" where "n in ZZ$

So

when

$=>3x=2npi+x" where "n in ZZ$

$=>2x=2npi" where "n in ZZ$

$=>x=npi" where "n in ZZ$

Again when

$=>3x=2npi-x" where "n in ZZ$

$=>4x=2npi" where "n in ZZ$

$=>x=(npi)/2" where "n in ZZ$