Question

Найти d²z: z=tg(3x·y)

Answer 1

$displaystyle mathrm{d^2z}={partial^2zoverpartial{x^2}}mmathrm{dx^2}+2{partial^2zoverpartial{x}partial{y}}mathrm{dx}mathrm{dy}+{partial^2zoverpartial{y^2}}mathrm{dy^2}={partial^2zoverpartial{x^2}}mmathrm{dx^2}+2{partial^2zoverpartial{y}partial{x}}mathrm{dy}mathrm{dx}+{partial^2zoverpartial{y^2}}mathrm{dy^2}$