Q20 of 25 Page 3

Prove that

As we know cos (x + y) = cos x cos y – sin x sin y


cos (x – y) = cos x cos y + sin x sin y


⇒ cos (x + y) + cos (x – y ) = 2 cos x cos y


So,




]



As we know cos(π -x) = - cos x



= 0


= RHS


Hence proved


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