Question
Integrate the function: $\frac{{\left( {x + 1} \right){{\left( {x + \log x} \right)}^2}}}{x}$
Putting x + log x = t
$ \Rightarrow 1 + \frac{1}{x} = \frac{{dt}}{{dx}}$
$ \Rightarrow \frac{{x + 1}}{x} = \frac{{dt}}{{dx}}$
$\Rightarrow \left( {\frac{{x + 1}}{x}} \right)dx = dt$
$\therefore$ From eq. (i), $I = \int {{t^2}dx} $
$= \frac{{{t^3}}}{3} + c$
$= \frac{1}{3}{\left( {x + \log x} \right)^3} + c$
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$\tan^{-1}\Bigg(\frac{1}{3}\Bigg)+\tan^{-1}\Bigg(\frac{1}{5}\Bigg)+\tan^{-1}\Bigg(\frac{1}{7}\Bigg)+\tan^{-1}\Bigg(\frac{1}{8}\Bigg)=\frac{\pi}{4}.$