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

  • question_answer
    The value of \[\int_{0}^{\pi /2}{\frac{dx}{1+{{\tan }^{3}}x}}\] is    [IIT 1993; DCE 2000, 01]

    A)                 0             

    B)                 1

    C)                 \[\frac{\pi }{2}\]              

    D)                 \[\frac{\pi }{4}\]

    Correct Answer: D

    Solution :

               \[I=\int_{0}^{\pi /2}{\frac{dx}{1+{{\tan }^{3}}x}=\int_{0}^{\pi /2}{\frac{{{\cos }^{3}}x}{{{\sin }^{3}}x+\cos {{x}^{3}}}}}dx\]   ?..(i)                       \[=\int_{0}^{\pi /2}{\frac{{{\sin }^{3}}x}{{{\cos }^{3}}x+{{\sin }^{3}}x}dx}\]                      .....(ii)                                 Adding (i) and (ii), we get \[2I=\int_{0}^{\pi /2}{dx\Rightarrow I=\frac{\pi }{4}.}\]


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