How to display a equation?
My code TeX
\begin{eqnarray*}
\displaystyle\int f'(x)\ln x\mathrm{\,d}x &=& \displaystyle\int\ln x\mathrm{\,d}\left[f(x)\right] = f(x)\ln x - \displaystyle\int f(x)\mathrm{\,d}\left(\ln x\right) = f(x)\ln x -\displaystyle\int\dfrac{f(x)}{x}\mathrm{\,d}x\\
&=& -\dfrac{1}{x^2}\ln x-\dfrac{1}{2x^2}+C = -\left(\dfrac{\ln x}{x^2}+\dfrac{1}{2x^2}\right)+C.
\end{eqnarray*}