au/ax=au/aξaξ/ax+au/aηaη/ax+au/aζaζ/ax=au/aξ-au/aη-au/aζ
au/ay=au/aξaξ/ay+au/aηaη/ay+au/aζaζ/ay=au/aη
au/az=au/aξaξ/az+au/aηaη/az+au/aζaζ/az=au/aζ
所以au/ax+au/ay+au/az=au/aξ-au/aη-au/aζ+au/aη+au/ζ=au/aξ=0
命题得证
u=x,v=y/x
那么得到az/ax=az/auau/ax+az/avav/ax
=az/au+az/av(-y/x²)
而az/ay=az/auau/ay+az/avav/ay
=az/av1/x
代入xaz/ax+yaz/ay=z中
得到z=uaz/au+az/av(-y/x)+az/avy/x=uaz/au
az/ax=az/auau/ax+az/avav/ax=az/au+az/av(-y/x^2)
az/ay=az/auau/ay+az/avav/ay=az/av(1/x)
xaz/ax+yaz/ay=xaz/au+az/av(-y/x)+az/av(y/x)=xaz/au=uaz/au
xaz/ax+yaz/ay=z
即z=uaz/au
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