JEE Main & Advanced Mathematics Definite Integration Question Bank Fundamental definite integration, Definite integration by substitution

  • question_answer
    \[\int_{0}^{\pi /2}{\frac{\cos x}{(1+\sin x)(2+\sin x)}}\,dx=\]                                 [UPSEAT 1999]

    A)                 \[\log \frac{4}{3}\]

    B)                 \[\log \frac{1}{3}\]

    C)                 \[\log \frac{3}{4}\]

    D)                 None of these

    Correct Answer: A

    Solution :

               Put \[\sin x=t\Rightarrow \cos x\,dx=dt,\] so that reduced integral is \[\int_{0}^{1}{\left( \frac{1}{1+t}-\frac{1}{2+t} \right)\,\,dt=[\log (1+t)-\log (2+t)]_{0}^{1}}\]                                                                  \[=\log \frac{2}{3}-\log \frac{1}{2}=\log \frac{4}{3}\].


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