MCQ
The differential coefficient of $f[\log (x)]$ when $f(x) = \log x$ is
  • A
    $x\log x$
  • B
    ${x \over {\log x}}$
  • ${1 \over {x\log x}}$
  • D
    ${{\log x} \over x}$

Answer

Correct option: C.
${1 \over {x\log x}}$
c
(c) $\because f(x)=\log x$ ; 

$\therefore f[\log x] = \log \log x$ 

$f'[\log x] = \frac{1}{{\log x}}.\frac{d}{{dx}}\log x = \frac{1}{{x\log x}}$.

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