JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2007

  • question_answer
        If\[2a+3b+6c=0,\] then at least one root of the equation\[a{{x}^{2}}+bx+c=0\]lies in the interval

    A)  (0, 1)

    B)  (1, 2)

    C)  (2, 3)                                    

    D)  (1, 3)

    Correct Answer: A

    Solution :

                     Let         \[f(x)=a{{x}^{2}}+bx+c\] \[\Rightarrow \]               \[f(x)=\frac{a{{x}^{3}}}{3}+\frac{b{{x}^{2}}}{2}+cx+d\] \[\Rightarrow \]               \[f(x)=\frac{2a{{x}^{3}}+3b{{x}^{2}}+6cx+6d}{6}\] \[\Rightarrow \]               \[f(1)=\frac{2a+3b+6c+6d}{6}=\frac{6d}{6}=d\]                                                 \[(\because 2a+3b+6c=0)\]                 \[f(0)=\frac{6d}{6}=d\] \[\therefore \]  \[f(0)=f(1)\] \[\Rightarrow \]\[f(x)\]will vanish at least once between 0 and 1. \[\therefore \]One of the roots of\[a{{x}^{2}}+bx+c=0\]lies between 0 and 1.                  


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