记:z = f(x,y) = (x^2+y^2)e^[(x^2+y^2)/xy] = u(x,y) e^[u(x,y)/v(x,y)]
其中: u(x,y) = (x^2+y^2);
v(x,y) = xy;
全微分: dz = df(x,y) = [∂f(x,y)/∂x] dx + [∂f(x,y)/∂y] dy
∂f(x,y)/∂x = ∂u(x,y)/∂x e^(u/v) + u e^(u/v) ∂(u/v)/∂x
∂f(x,y)/∂y = ∂u(x,y)/∂y e^(u/v) + u e^(u/v) ∂(u/v)/∂y
∂f(x,y)/∂x = e^[(x^2+y^2)/xy] [2x + (x^2+y^2) (2x-(x^2+y^2))/(x^2y)]
∂f(x,y)/∂y = e^[(x^2+y^2)/xy] [2y + (x^2+y^2) (2y-(x^2+y^2))/(xy^2)]
这是 z对x,y的两个偏导数。
z的全微分:
dz = df(x,y) = e^[(x^2+y^2)/xy] {[2x + (x^2+y^2) (2x-(x^2+y^2))/(x^2y)] dx +
+ [2y + (x^2+y^2) (2y-(x^2+y^2))/(xy^2)] dy }