The general solution of the equation cos⁡xcos⁡6x=−1, is

The general solution of the equation cosxcos6x=1, is

  1. A

    x=(2n+1)π,nZ

  2. B

    x=2nπ,nZ

  3. C

    x=(2n1)π,nZ

  4. D

    none of these

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    Solution:

    We have,

    cosxcos6x=1 2cosxcos6x=2 cos7x+cos5x=2cos7x=1

    and  cos 5 x=-1 

    The value of x satisfying these two equations simultaneously and lying between 0 and 2 π is π. Therefore, the general solution is given by

    x=2nπ+π,nZx=(2n+1)π,nZ

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