Evaluate
$I=\int_{1}^{e}\dfrac{\ln x(\ln x+1)}{(1+x+\ln x)^3}dx$
Thank you very much
Evaluate
$I=\int_{1}^{e}\dfrac{\ln x(\ln x+1)}{(1+x+\ln x)^3}dx$
Thank you very much
First make a change of variable to get the integral $ I = \int_0^1 \frac{\mathrm{e}^y y \left( y + 1 \right)}{\left( \mathrm{e}^y + y + 1 \right)^3} \mathrm{d} y $ and notice that the integrand is obtained as a derivative of $ - \tfrac{\left( y + 1 \right)^2}{2 \left( \mathrm{e}^y + y + 1 \right)^2} $ Now apply the fundamental theorem of calculus to get $ I = \frac{1}{8} - \frac{2}{\left( 2 + \mathrm{e} \right)^2} $
$I=\int\limits_{1}^{e}\frac{\ln x(\ln x+1)}{{x}^{3}(\frac{1}{x}+1+\frac{\ln x}{x})^3}\,\mathrm dx$
Set: $t=\frac{1}{x}+1+\frac{\ln x}{x}$
So $t-1=\frac{\ln x+1}{x}$
And $\mathrm dt=-\frac{\ln x}{x^2}\mathrm dx$
When $x=1$, $t=2$
When $x=e$, $t=\frac{2+e}{e}$
So $I=-\int_{2}^{\frac{2+e}{e}}\frac{t-1}{t^3}\,dt$
$I=\int_{1}^{e}\frac{\ln x(\ln x+1)}{(1+x+\ln x)^3}dx$
Let, $\ln{x}=t$, then, $x=e^{t},\ln x=t$
$dx=e^tdt$
$I=\int_{0}^{1}\frac{e^t(t)(t+1)}{(1+e^t+t)^3}dt$