Question #0373f

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Answer 1 · 2017-03-11T07:12:32

#sin 2x sin x - cos 2x cos x =-cos x#

# =>cos 2x cos x-sin 2x sin x =cos x#

# =>cos (2x + 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#