MCQ
The value of $\int_{\,0}^{\,\pi /2} {\frac{{{e^{{x^2}}}}}{{{e^{{x^2}}} + {e^{{{\left( {\frac{\pi }{2}\,\, - \,\,x} \right)}^2}}}}}dx} $ is
  • $\pi /4$
  • B
    $\pi /2$
  • C
    ${e^{{\pi ^2}/16}}$
  • D
    ${e^{{\pi ^2}/4}}$

Answer

Correct option: A.
$\pi /4$
a
(a) $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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