Manipal Engineering Manipal Engineering Solved Paper-2013

  • question_answer
    The number of solutions of the equation\[1+\sin x\cdot {{\sin }^{2}}\frac{x}{2}=0\]in\[[-\pi ,\,\,\pi ]\]is

    A)  zero                     

    B)  1

    C)  2                            

    D)         3

    Correct Answer: A

    Solution :

    \[1+\sin x\cdot {{\sin }^{2}}\frac{x}{2}=0\] \[\Rightarrow \]               \[2+2\sin x\cdot {{\sin }^{2}}\frac{x}{2}=0\] \[\Rightarrow \]               \[2+\sin x(1-\cos x)=0\] \[\Rightarrow \]               \[4+2\sin x(1-\cos x)=0\] \[\Rightarrow \]               \[4+2\sin x-\sin 2x=0\] \[\Rightarrow \]               \[\sin 2x=2\sin x+4\] Above is not possible for any value of\[x\]as LHS has maximum value 1 and RHS has value 2. Hence, there is no solution.


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