大学数学真题辨析

d(x+y+z)=de^(-x-y-z)

dx+dy+dz=e^(-x-y-z)d(-x-y-z)

dx+dy+dz=e^(-x-y-z)(-dx-dy-dz)

[e^(-x-y-z)+1]dz=-[e^(-x-y-z)+1]dx-[e^(-x-y-z)+1]dy

dz=-dx-dy