Question

对d(x.y)求微分?

Answer 1

u = f(x,y)

du = (∂f/∂x)dx + (∂f/∂y)dy

比如

u = f(x,y) = x^2 + 3xy + y^2

∂u/∂x = 2x + 3y

∂u/∂y = 3x + 2y

du = (2x + 3y)dx + (3x + 2y)dy