CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2005

  • question_answer
    If\[y={{a}^{x}}.{{b}^{2x-1}},\]then\[\frac{{{d}^{2}}y}{d{{x}^{2}}}\]is:

    A)  \[{{y}^{2}}.\log a{{b}^{2}}\]                       

    B)  \[y.\log a{{b}^{2}}\]

    C)  \[{{y}^{2}}\]                     

    D)         \[y.{{(\log {{a}^{2}}b)}^{2}}\]

    E)  \[y.{{(\log a{{b}^{2}})}^{2}}\]

    Correct Answer: E

    Solution :

    \[\because \]     \[y={{a}^{x}}{{b}^{2x-1}}\] Taking log on both sides, we get \[log\text{ }y=x\text{ }log\text{ }a+(2x-1)log\text{ }b\] On differentiating w.r.t.\[x,\]we get                 \[\frac{1}{y}=\frac{dy}{dx}=\log a+\log {{b}^{2}}\] \[\frac{dy}{dx}=y\log a{{b}^{2}}\] Again differentiating, we get                 \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=\frac{dy}{dx}\log a{{b}^{2}}=y{{(\log \,a{{b}^{2}})}^{2}}\]


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