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

  • question_answer
    If [x] denotes the greatest integer less than or equal to x, then the value of \[\int_{\,1}^{\,5}{\,\,[|x-3|]\,dx}\] is                 [Roorkee 1999]

    A)                 1             

    B)                 2

    C)                 4             

    D)                 8

    Correct Answer: B

    Solution :

               \[I=\int_{1}^{5}{\,[|x-3|]}\,dx\]\[\Rightarrow I=\int_{1}^{3}{[-(x-3)]\,dx+\int_{3}^{5}{\,\left[ (x-3) \right]}\,dx}\]                 \[\Rightarrow I=\int_{1}^{2}{\,[-(x-3)}]dx+\,\int_{2}^{3}{\,[-(x-3)]dx+}\int_{3}^{4}{[x-3]\,dx+\int_{4}^{5}{\,[x-3]\,dx}}\]                 \[\Rightarrow I=\int_{1}^{2}{\,dx}+\int_{2}^{3}{0\,dx+\int_{3}^{4}{0\,dx+\int_{4}^{5}{\,dx}}}\]\[=[x]_{1}^{2}+[x]_{4}^{5}\]                      \[\Rightarrow I=(2-1)+(5-4)=2\].


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