JEE Main & Advanced Sample Paper JEE Main - Mock Test - 5

  • question_answer
    If \[\int{{{e}^{x}}(1+x).\,{{\sec }^{2}}(x{{e}^{x}})\,dx=f(x)+}\]constant, then \[f(x)\] is equal to

    A) \[\cos \,(x{{e}^{x}})\]                      

    B) \[sin\,(x{{e}^{x}})\]

    C) \[2{{\tan }^{-1}}(x)\]                      

    D) \[\tan \,(x{{e}^{x}})\]

    Correct Answer: D

    Solution :

    Given that \[\int{{{e}^{x}}\left( 1+x \right).{{\sec }^{2}}\left( x{{e}^{x}} \right)dx=f(x)+\,\,}\text{constant}\]
    Put \[x{{e}^{x}}=t\] in L.H.S. \[\Rightarrow \,\left( {{e}^{x}}+x{{e}^{x}} \right)dx=dt\]
    \[\because \] L.H.S. \[=\int{{{\sec }^{2}}\,t\,dt=\tan t+\,}\text{constant}\]
    \[\Rightarrow \,\,\,\,\tan \,\,(x\,{{e}^{x}})+constant=f(x)+constant\]
    \[\Rightarrow \,\,f(x)=\tan \,(x{{e}^{x}})\]


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