JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2010

  • question_answer
        \[\int_{0}^{1}{\frac{({{x}^{\alpha }}-1)dx}{\log x}}\]equals

    A)  \[\frac{1}{\alpha +1}\]                 

    B)  \[\frac{1}{\alpha -1}\]

    C)  \[\alpha -1\]                                     

    D)  None of these

    Correct Answer: D

    Solution :

                    Let\[I=\int_{0}^{1}{\frac{({{x}^{\alpha }}-1)dx}{\log x}}\] \[\frac{dI}{d\alpha }=\int_{0}^{1}{\frac{{{x}^{\alpha }}\log x}{\log x}}dx\] \[\Rightarrow \]               \[\frac{dI}{d\alpha }=\int_{0}^{1}{{{x}^{\alpha }}dx}\]                                 \[=\left[ \frac{{{x}^{\alpha +1}}}{\alpha +1} \right]_{0}^{1}\] \[\Rightarrow \]               \[\frac{dI}{d\alpha }=\frac{1}{\alpha +1}\] \[\Rightarrow \]               \[dI=\frac{1}{\alpha +1}d\alpha \] On integrating, we get                 \[I=\log (\alpha +1)+c\] Now, if\[\alpha =0,\]then                 \[I=\int_{0}^{1}{\frac{({{x}^{0}}-1)}{\log x}}dx\] \[\Rightarrow \]               \[I=\int_{0}^{1}{0\,dx}=0\] \[\therefore \]From Eq. (i),                 \[0=\log 1+c\] \[\Rightarrow \]               \[c=0\] Hence, \[I=log(\alpha +1)\]


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