d（x+y+z）=d√(x+y+z)dx+dy+dz=1/2√(xyz) d(xyz)dx+dy+dz=1/2√(xyz) (yzdx+xzdy+xydz)(1-xy/(2√xyz))dz=[yz/(2√xyz)-1]dx+[xz/(2√xyz)-1]dydz=[yz/(2√xyz)-1]/(1-xy/(2√xyz))dx+[xz/(2√xyz)-1]/(1-xy/(2√x...