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  3. JEE Main & Advanced

JEE Main & Advanced Sample Paper JEE Main Sample Paper-25

  • question_answer
    If \[\cos A,\sin B,\sin iA\] (taken in that order) are in G.P., then the roots of the equation \[{{x}^{2}}+2x\cot B+1=0\] are

    A)  real and distinct            

    B)  real

    C)  imaginary        

    D)  real and equal

    Correct Answer: B

    Solution :

    \[{{\sin }^{2}}B=\sin A\cos A\]\[\Rightarrow \,\,\cos 2B=1-\sin 2A\ge 0\]and \[D=4({{\cot }^{2}}B-1)\,=4\,\cos 2B.\cos e{{c}^{2}}\ge 0\]\[\Rightarrow \] roots are real.


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