The number of values of x lying in the internal (−π,π) which satisfy the equation 81+|cos⁡x|+cos2⁡x+cos3⁡x+…∞=43,is 

The number of values of x lying in the internal (π,π) which satisfy the equation 81+|cosx|+cos2x+cos3x+=43,is 

  1. A

    3

  2. B

    4

  3. C

    5

  4. D

    6

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    Solution:

    Now,1+|cosx|+cos2x+cos3x+=11|cosx|

     811|cosx|=43

    31|cosx|=261=22|cosx||cosx|=12cosx=±12x=π3,π3,2π3,2π3

     Number of solutions =4

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