JEE Main & Advanced Sample Paper JEE Main Sample Paper-6

  • question_answer
    If a, b, c are non-zero real numbers and \[a{{z}^{2}}+bz+c+i=0\] has purely imaginary roots, then a equals

    A)  be                         

    B)  \[{{b}^{2}}c\]

    C)  \[-{{b}^{2}}c\]                                 

    D)  \[\frac{1}{2}{{b}^{2}}c\]

    Correct Answer: B

    Solution :

    Let i\[\alpha \], where \[\alpha \] is purely real be one of the imaginary roots. Then, \[-a{{\alpha }^{2}}+ib\alpha +c+i=0\] \[\Rightarrow \]\[c=a{{\alpha }^{2}},1+b\alpha =0\] \[\Rightarrow \]\[{{\alpha }^{2}}=\frac{c}{a},\alpha =\frac{-1}{b}\] \[\Rightarrow \]\[\frac{1}{{{b}^{2}}}=\frac{c}{a}\Rightarrow a={{b}^{2}}c\]\[\Rightarrow \]


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