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

  • question_answer
    If n is a positive integer and [x] is the greatest integer not exceeding x, then \[\int_{0}^{n}{\,\,\{x-[x]\}\,dx}\] equals

    A)                 \[{{n}^{2}}/2\]  

    B)                 \[n(n-1)/2\]

    C)                 \[n\,/\,2\]          

    D)                 \[\frac{{{n}^{2}}}{2}-n\]

    Correct Answer: C

    Solution :

               \[x-[x]\] is a periodic function with period 1.            \[\therefore \int_{0}^{n}{\left\{ x-[x] \right\}\,dx=n\int_{0}^{1}{(x-[x])\,\,dx}}\]                                 \[=n\left[ \int_{0}^{1}{x\,\,dx-\int_{0}^{1}{[x]\,dx}} \right]\]\[=n\left[ \left( \frac{{{x}^{2}}}{2} \right)_{0}^{1}-0 \right]=\frac{n}{2}\].


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