JCECE Engineering JCECE Engineering Solved Paper-2005

  • question_answer
    If \[y={{\log }^{n}}x\], where\[{{\log }^{n}}\]means\[\log \log \log ...\](repeated \[n\] times), then\[x\log x{{\log }^{2}}x{{\log }^{3}}x...{{\log }^{n-1}}x{{\log }^{n}}x\frac{dy}{dx}\]is equal to:

    A) \[\log x\]                            

    B) \[x\]

    C) \[\frac{1}{\log x}\]                          

    D) \[{{\log }^{n}}x\]

    Correct Answer: D

    Solution :

    Given that,                 \[y={{\log }^{n}}x\] \[\therefore \]\[x\log x{{\log }^{2}}x{{\log }^{3}}x...{{\log }^{n-1}}x{{\log }^{n}}x\times \frac{dy}{dx}\] \[=x\log x{{\log }^{2}}x{{\log }^{3}}x...{{\log }^{n-1}}x{{\log }^{n}}x\] \[\times \frac{1}{x\log x{{\log }^{2}}x{{\log }^{3}}x...{{\log }^{n-1}}x}\] \[={{\log }^{n}}x\]


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