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

  • question_answer
    The value of \[\int_{2}^{3}{\frac{\sqrt{x}}{\sqrt{5-x}+\sqrt{x}}}\,dx\] is [IIT 1994; Kurukshetra CEE 1998]

    A)                 1             

    B)                 0

    C)                 \[-1\]

    D)                 \[\frac{1}{2}\]

    Correct Answer: D

    Solution :

               \[I=\int_{2}^{3}{\frac{\sqrt{x}}{\sqrt{5-x}+\sqrt{x}}dx}\]                                   ?..(i)            Using the property \[I=\int_{a}^{b}{f(x)dx=\int_{a}^{b}{f(a+b-x)}dx}\]            i.e., change in\[x=(2+3-x)=5-x\]or \[dx=-dx\]     \[\therefore I=\int_{3}^{2}{\frac{\sqrt{5-x}}{\sqrt{x}+\sqrt{5-x}}}(-dx)\]\[=\int_{2}^{3}{\frac{\sqrt{5-x}}{\sqrt{5-x}+\sqrt{x}}dx}\]  ?..(ii)            Adding (i) and (ii), \[2I=\int_{2}^{3}{\frac{\sqrt{x}+\sqrt{5-x}}{\sqrt{5-x}+\sqrt{x}}dx=\int_{2}^{3}{1dx}}\]                                                                   \[=[x]_{2}^{3}=3-2=1\Rightarrow I=\frac{1}{2}\].


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