JEE Main & Advanced Mathematics Differentiation Question Bank Differentiation by Substitution

  • question_answer
    If \[y={{x}^{3}}\log {{\log }_{e}}(1+x)\], then \[{y}''\,(0)\] equals [AMU 1999]

    A)            0

    B)            ? 1

    C)            \[6\,\,\log {{}_{e}}\,2\]

    D)            6

    Correct Answer: A

    Solution :

               \[y={{x}^{3}}\log {{\log }_{e}}(1+x)\]            Þ  \[{y}'=3{{x}^{2}}\log {{\log }_{e}}\,(1+x)+\frac{{{x}^{3}}}{1+x}.\frac{1}{{{\log }_{e}}(1+x)}\]            Þ  \[{y}''=6x\log {{\log }_{e}}(1+x)+\frac{3{{x}^{2}}}{{{\log }_{e}}(1+x)}.\frac{1}{(1+x)}\]             \[-\frac{{{x}^{3}}}{{{(1+x)}^{2}}{{\log }_{e}}(1+x)}-\frac{{{x}^{3}}}{{{(1+x)}^{2}}}.\frac{1}{{{[{{\log }_{e}}(1+x)]}^{2}}}+\frac{3{{x}^{2}}}{(1+x){{\log }_{e}}(1+x)}\]                    Þ  \[{y}''(0)=0\].


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