Q. The anti-derivative of $f(x) = \log{(\log{x) + ({\log{x)}}^{- 2}}}$ whose graph passes through $(e,e)$, is

A) $x\lbrack\log{(\log{x) + (\log{{x)}^{- 1}\rbrack}}}$
B) $x\lbrack{- log}{(\log{x) + (\log{{x)}^{- 1}\rbrack}}} + e$
C) $x\lbrack\log{(\log{x) - (\log{{x)}^{- 1}\rbrack + 2e}}}$
D) None of the above
Explanation

(c)
An anti-derivative of $f(x)$
$= F(x)$
$= \int_{}^{}{\lbrack\log{(\log{x) + \left( {\log{x)}}^{- 2} \right\rbrack dx + c}}}$
$= x\log{(\log{x) - \int_{}^{}{\frac{x}{x\log x}dx + \int_{}^{}{({\log{x)}}^{- 2}dx + c}}}}$
(integrating by parts the first integral)
$= x\log{(\log{x) - \lbrack x({\log{x)}}^{- 1} + \int_{}^{}{\left( {\log{x)}}^{- 2}dx \right\rbrack + \int_{}^{}\left( \log x \right)^{- 2}dx + c}}}$
[again integrating by parts $({\log{x)}}^{- 1}$]
$= x\log{(\log{x) - x({\log{x)}}^{- 1} + c}}$
On putting $x = e$, we have, $e = 0 - e + c$ so, $c = 2e$
Thus, $F(x) = x\lbrack\log{(\log{x) - \left( {\log{x)}}^{- 1} \right\rbrack + 2e}}$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.

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