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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
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
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