deletions | additions       diff --git a/untitled.tex b/untitled.tex  index a0a1122..4a89b44 100644  --- a/untitled.tex  +++ b/untitled.tex 
...
Therefore, it follows that   \begin{eqnarray}  Df(x) &=& \left[ \frac{\partial \|x\|_{\ell_2}^2}{\partial x_1}, \dots, \frac{\partial \|x\|_{\ell_2}^2}{\partial x_n} \right] \nonumber\\  &=& \left[2x_1, \ldots, 2x_n \right] \nonumber\\  &=& 2x. \nonumber  \end{eqnarray}