$$f ( x ) = \cot ( \sin ( \sqrt { x ^ { 2 } + x ^ { 2 } } ) )$$
$\cot(\sin(\sqrt{2}|x|))$
$-\frac{\sqrt{2}sign(x)\cos(\sqrt{2}|x|)}{\left(\sin(\sin(\sqrt{2}|x|))\right)^{2}}$
