MCQ
$\int {\left[ {\log \left( {\log x} \right) + {{\left( {\log x} \right)}^{ - 2}}} \right]} \,\,dx =\ ........$
  • A
    $x\,\log \left( {\log x} \right)$
  • B
    $x\log \left( {\log x} \right) + \frac{x}{{\left( {\log x} \right)}}$
  • $x\log \left( {\log x} \right) - \frac{x}{{\left( {\log x} \right)}}$
  • D
    એક પણ નહીં.

Answer

Correct option: C.
$x\log \left( {\log x} \right) - \frac{x}{{\left( {\log x} \right)}}$
$I = \int \left[ \log (\log x) + (\log x)^{-2} \right]dx$
$I = \int2^t \left[ \log t + \frac{1}{t^2}\right] dt$
$\begin{cases}\log x = t \\x= e^t\\dx = e^tdt\end{cases}$
$= \int e^t \left[ \log t + \frac{1}{t}\right] - e^t \left(\frac{1}{t} -\frac{1}{t^2}\right)dt$
$= e^t \log t - e^t \frac{1}{t}$
$= x \log (\log x) - \frac{x}{\log x}$

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