JEE Main & Advanced Mathematics Definite Integration Question Bank Properties of Definite Integration

  • question_answer
    The value of \[\int_{\,0}^{\,\pi /2}{\frac{{{e}^{{{x}^{2}}}}}{{{e}^{{{x}^{2}}}}+{{e}^{{{\left( \frac{\pi }{2}\,\,-\,\,x \right)}^{2}}}}}dx}\] is    [AMU 1999]

    A)                 \[\pi /4\]             

    B)                 \[\pi /2\]

    C)                 \[{{e}^{{{\pi }^{2}}/16}}\]            

    D)                 \[{{e}^{{{\pi }^{2}}/4}}\]

    Correct Answer: A

    Solution :

               \[I=\int_{0}^{\pi /2}{\frac{{{e}^{{{x}^{2}}}}\,\,\,\,\,\,dx}{{{e}^{{{x}^{2}}}}+{{e}^{\left( \frac{\pi }{2}\,\,-x \right)}}^{2}}}\]and \[I=\int_{0}^{\pi /2}{\frac{{{e}^{{{\left( \frac{\pi }{2}-x \right)}^{2}}}}\,\,\,\,\,\,dx}{{{e}^{{{\left( \frac{\pi }{2}\,-x \right)}^{2}}}}+{{e}^{{{x}^{2}}}}}}\]                    \[\left[ \because \int_{0}^{a}{f(x)dx=\int_{0}^{a}{f(a-x)dx}} \right]\]                 \[\Rightarrow 2I=\int_{0}^{\pi /2}{1dx=(x)_{0}^{\pi /2}}\] \[\Rightarrow I=\frac{\pi }{4}\].


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