u=ln(xy+z)求du=
问题描述：
u=ln(xy+z)求du=
答
u=ln(xy+z)
du=d[ln(xy+z)]/dx*dx+d[ln(xy+z)]/dy*dy+d[ln(xy+z)]/dz*dz
=y/(xy+z)*dx+x/(xy+z)*dy+1/(xy+z)*dz
=(ydx+xdy+dz)/(xy+z)