[pmath size=16]vec{del}f(x, ~y) ~ = ~ {partial{f}}/{partial{x}}hat{i} ~ + ~ {partial{f}}/{partial{y}} hat{j}[/pmath] 

[pmath size=16]{del}f(x, ~y) ~ = ~ {partial{f}}/{partial{x}}i ~ + ~ {partial{f}}/{partial{y}} j[/pmath]