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  3. CEE Kerala Engineering

CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2009

  • question_answer
    If\[2-i\]is  a root of the  equation \[a{{x}^{2}}+12x+b=0\](where a and b are real), then the value of ab is equal to

    A)  45                                         

    B)  15

    C)  \[-15\]                

    D)         \[-45\]

    E)  25

    Correct Answer: A

    Solution :

    If one root is\[2-i,\]then the other root will be \[2+i.\] Given equation is\[a{{x}^{2}}+12x+b=0\] \[\therefore \]  \[2-i+2+i=\frac{-12}{a}\] \[\Rightarrow \]               \[a=-3\] and        \[(2-i)(2+i)=\frac{b}{a}\] \[\Rightarrow \]               \[5=\frac{b}{-3}\Rightarrow b=-15\] \[\therefore \]  \[ab=-3\times (-15)=45\]


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