JEE Main & Advanced Mathematics Definite Integration Question Bank Summation of series by Definite Integration, Gamma function, Leibnitz's rule

  • question_answer
    \[\underset{n\to \infty }{\mathop{\lim }}\,\frac{{{1}^{p}}+{{2}^{p}}+{{3}^{p}}+.....+{{n}^{p}}}{{{n}^{p+1}}}=\]   [AIEEE 2002]

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

    B)                 \[\frac{1}{1-p}\]

    C)                 \[\frac{1}{p}-\frac{1}{p-1}\]       

    D)                 \[\underset{x\to 0-}{\mathop{\lim }}\,f(x)=0\]

    Correct Answer: A

    Solution :

               \[\underset{n\to \infty }{\mathop{\lim }}\,\frac{{{1}^{p}}+{{2}^{p}}+{{3}^{p}}+.....+{{n}^{p}}}{{{n}^{p+1}}}\]= \[\underset{n\to \infty }{\mathop{\lim }}\,\sum\limits_{r=1}^{n}{\left[ \frac{{{r}^{p}}}{{{n}^{p+1}}} \right]}\]                 = \[\underset{n\to \infty }{\mathop{\lim }}\,\frac{1}{n}\sum\limits_{r=1}^{n}{{{\left( \frac{r}{n} \right)}^{p}}}=\int_{0}^{1}{{{x}^{p}}dx}=\left[ \frac{{{x}^{p+1}}}{p+1} \right]_{0}^{1}=\frac{1}{p+1}\].


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