# Cross partial derivatives with LaTeX

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?

• \frac{\partial^2 f}{\partial y \partial x} = \frac{\partial}{\partial y} \biggl( \frac{\partial f}{\partial x} \biggr) = ..., performed inside a math environment. p.s and while pronounced like "Latek, it is actually spelled with a final "X", as in "LaTeX". – Steven B. Segletes May 26 '17 at 18:44
• @StevenB.Segletes it's not pronounced like "Latek" as far as I know... But I think that's what is acceptable for an English speaker :) – Skillmon May 26 '17 at 18:50
• @Skillmon It's pronounced lah-teck or lay-teck. – sodd May 26 '17 at 19:05
• @hooy since the X is not an X but a greek \chi it should be pronounced like a greek \chi which is not pronounced 'ck' as far as I know, but I totally understand if it's not pronounced that way (as a German I don't pronounce it correct, too, most of the time). – Skillmon May 26 '17 at 19:07
• @Skillmon I'm very aware, I just know Leslie Lamport himself wrote about this in this book LaTeX: A document Preparation System. – sodd May 26 '17 at 19:18

\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.