JEE Main & Advanced Sample Paper JEE Main Sample Paper-12

  • question_answer
    The value of the definite integral \[\int\limits_{0}^{3\pi /4}{[(1+x)\sin x+(1-x)\cos x]}dx\]is

    A)  \[2\tan \frac{2\pi }{8}\]                               

    B)  \[2\tan \frac{\pi }{4}\]

    C)  \[2\tan \frac{\pi }{8}\]                 

    D)  0

    Correct Answer: A

    Solution :

     \[I=\int\limits_{0}^{3\pi /4}{(\sin x+\cos x)}dx+\int\limits_{0}^{3\pi /4}{\underbrace{x}_{I}\underbrace{(\sin x-\cos x)}_{II}dx}\] \[=\int\limits_{0}^{3\pi /4}{(\sin x+\cos x)}dx+\underbrace{x(-\cos x-\sin x)|_{0}^{3\pi /4}}_{zero}\] \[+\int\limits_{0}^{3\pi /4}{(\sin x+\cos x)}dx\] \[=2\int\limits_{0}^{3\pi /4}{(\sin x+\cos x)}dx=-2\]


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