CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2009

  • question_answer
    The value of\[\int_{1}^{e}{{{10}^{{{\log }_{e}}x}}}dx\]is equal to

    A)  \[10{{\log }_{e}}(10e)\]

    B)                         \[\frac{10e-1}{{{\log }_{e}}10e}\]

    C)  \[\frac{10e}{{{\log }_{e}}10e}\]

    D)         \[(10e){{\log }_{e}}(10e)\]

    E)  \[3\,sq\,unit\]

    Correct Answer: B

    Solution :

    Let \[I=\int_{1}^{e}{{{10}^{{{\log }_{e}}x}}dx}\] Again, let \[{{I}_{1}}=\int{{{10}^{{{\log }_{e}}x}}}dx\] \[\Rightarrow \] \[{{I}_{1}}=x{{.10}^{{{\log }_{e}}x}}-\int{x{{.10}^{{{\log }_{e}}x}}.\frac{{{\log }_{e}}10}{x}}dx\] \[\Rightarrow \] \[{{I}_{1}}=x{{10}^{{{\log }_{e}}x}}-\int{{{10}^{{{\log }_{e}}x}}{{\log }_{e}}10\,}dx\] \[\Rightarrow \] \[(1+{{\log }_{e}}10){{I}_{1}}=x{{10}^{{{\log }_{e}}x}}\] \[\Rightarrow \]               \[{{I}_{1}}=\frac{x{{.10}^{{{\log }_{e}}x}}}{1+{{\log }_{e}}10}\] \[\therefore \]  \[I=\left[ \frac{x{{.10}^{{{\log }_{e}}x}}}{1+{{\log }_{e}}10} \right]_{1}^{e}\]                 \[=\left[ \frac{10e-1}{1+{{\log }_{e}}10} \right]\]                 \[=\frac{10e-1}{{{\log }_{e}}10e}\]


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