u=(x/y)^(1/z)lnu = (1/z)ln(x/y)(1/u)du = (-1/z^2)ln(x/y)dz + (1/z) [(1/x)dx - (1/y)dy]du ={ (-1/z^2)ln(x/y)dz + (1/z) [(1/x)dx - (1/y)dy] }(x/y)^(1/z)du|(1,1,1)={ 0 + (dx -dy) } (1)=dx -dy
