Question

Допоможіть знайти похідну!!!.

Answer 1

$\frac{\partial ^2z}{\partial x\partial y}=\frac{\partial }{\partial y}\frac{\partial }{\partial x}\left [ e^{3x}\cos 2y \right ]=\frac{\partial }{\partial y}\left [ 3e^{3x}\cos 2y \right ]=-\frac{\partial }{\partial y}\left [ 2y \right ]\sin 2y\cdot 3e^{3x}=-6e^{3x}\sin 2y$