JEE Main & Advanced JEE Main Paper (Held On 12-Jan-2019 Morning)

  • question_answer
    Integral \[\int_{{}}^{{}}{\cos (lo{{g}_{e}}x)}dx\]equals (where C is the constant of integration) [JEE Main Online Paper Held On 12-Jan-2019 Morning]

    A) \[\frac{x}{2}[sin(lo{{g}_{e}}x)-cos(lo{{g}_{e}}x)]+C\]

    B) \[x[cos(lo{{g}_{e}}x)-\sin (lo{{g}_{e}}x)]+C\]

    C) \[\frac{x}{2}[cos(lo{{g}_{e}}x)+\sin (lo{{g}_{e}}x)]+C\]

    D) \[x[cos(lo{{g}_{e}}x)+\sin (lo{{g}_{e}}x)]+C\]

    Correct Answer: C

    Solution :

    Let\[I=\int_{{}}^{{}}{\cos (lo{{g}_{e}}x)}dx\] \[\Rightarrow \]\[I=\cos (lo{{g}_{e}}x)x+\int_{{}}^{{}}{sin(lo{{g}_{e}}x)}dx\] \[\Rightarrow \]\[I=x\cos ({{\log }_{e}}x)+x\sin ({{\log }_{e}}x)x-\int_{{}}^{{}}{\cos ({{\log }_{e}}x)}dx\] \[\Rightarrow \]\[I=\frac{x}{2}[\cos ({{\log }_{e}}x)+\sin ({{\log }_{e}}x)]+C\]


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