KVPY Sample Paper KVPY Stream-SX Model Paper-9

  • question_answer
     If \[f\]and \[g\]are two continuous functions being even and odd respectively,  then\[\int\limits_{-a}^{a}{\frac{f(x)}{{{b}^{g(x)}}+1}dx}\]is equal to (a being any non-zero number and \[b\] is positive real number,\[b\ne 1\])

    A) Independent of \[f\]        

    B) Independent of  \[g\]

    C) Independent of both f and g

    D) None of these

    Correct Answer: B

    Solution :

    \[\int\limits_{-a}^{a}{xf(x)\,\,\,dx=\int\limits_{0}^{a}{f(x)\,dx+\int\limits_{0}^{a}{f(-x)dx}}}\]
    \[\therefore \int\limits_{-a}^{a}{\frac{f(x)}{{{b}^{g(x)}}+1}dx=\int\limits_{0}^{a}{\frac{f(x)}{{{b}^{g(x)}}+1}}}dx+\int\limits_{0}^{a}{\frac{f(-x)}{{{b}^{g(-x)}}+1}dx}\]
    \[=\int\limits_{0}^{a}{\frac{f(x)}{{{b}^{g(x)\,}}+1}dx=\int\limits_{0}^{a}{\frac{f(x)}{{{b}^{-g(x)}}+1}dx}}\]
                (\[\because f\]is a even and g is odd)
    \[=\int\limits_{0}^{a}{f(x)dx}\]Which is independent of g.


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