# [Tex/LaTex] Cross partial derivatives with LaTeX

equations

I'm trying to write something simple:

Not quite sure how to write out the second term (from the left) in LaTeX. Any suggestions please?

\documentclass{article}
$\frac{\partial^2 f}{\partial y \, \partial x} = \frac{\partial}{\partial y} \biggl( \frac{\partial f}{\partial x} \biggr) % = \frac{\partial}{\partial y} \left( \frac{\partial f}{\partial x} \right) = (f_x)_y = f_{xy} = \partial_{yx} f$

There is a difference in the spacing between using a \biggl(...\biggr) and \left(...\right) pair. Your choice, although the former is preferred.