The general solution of `cos x cos 6x =-1` isA. `x=(2n+1) pi, n in Z`B – InterviewSolution

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1.	The general solution of `cos x cos 6x =-1` isA. `x=(2n+1) pi, n in Z`B. `x=2n pi, n in Z`C. `x= n pi, n in Z`D. none of these
Answer» Correct Answer - A `cos x cos 6x=-1` or `2 cos x cos 6x=-2` or `cos 7x+ cos 5x=-2` or `cos 7x =-1 and cos 5x=-1` The value of x satisfying these two equations simultaneously and lying between 0 and `2pi` is `pi`. Therefore, the general solution is `x=2npi+pi, n in Z`. Thus, `x=(2n+1) pi, n in Z`

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