Question

Найти d²z: z=tg(3x·y)

Answer 1

$\displaystyle \mathrm{d^2z}={\partial^2z\over\partial{x^2}}\m\mathrm{dx^2}+2{\partial^2z\over\partial{x}\partial{y}}\mathrm{dx}\mathrm{dy}+{\partial^2z\over\partial{y^2}}\mathrm{dy^2}={\partial^2z\over\partial{x^2}}\m\mathrm{dx^2}+2{\partial^2z\over\partial{y}\partial{x}}\mathrm{dy}\mathrm{dx}+{\partial^2z\over\partial{y^2}}\mathrm{dy^2}$