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JEE Main & Advanced JEE Main Solved Paper-2016

  • question_answer
    If \[0\le x<2\pi ,\]then the number of real values of x, which satisfy the equation \[\cos x+\cos 2x+\cos 3x+\cos 4x=0,\]is :- [JEE Main Solved Paper-2016 ]

    A) 9                                             

    B)  3

    C)  5                                            

    D)  7

    Correct Answer: D

    Solution :

                    \[2\cos 2x\cos x+2\cos 3x\cos x=0\]                 \[\Rightarrow \]\[2\cos x(\cos 2x+\cos 3x)=0\] \[2\cos x2\cos 5x/2\cos x/2=0\] \[x=\frac{\pi }{2},\frac{3\pi }{2},\pi ,\frac{3\pi }{5},\frac{7\pi }{5},\frac{9\pi }{5}\] 7 Solutions


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