g和h均為x的函數

若你知道
d(g．h)/dx
=(dg/dx)．h + g．(dh/dx)

則同一法則
d(g/h)/dx
=d(g．1/h)/dx
=(dg/dx)．1/h + g．[d(1/h)/dx]
=[(dg/dx)．h]/h^2 + g．[d(h^-1)/dx]
=[(dg/dx)．h]/h^2 + g．[-(h^-2)．(dh/dx)]
=[(dg/dx)．h]/h^2 - [g． (dh/dx)]．(h^-2)
=[(dg/dx)．h]/h^2 –[g．(dh/dx)]/h^2
=[(dg/dx)．h – g．(dh/dx)]/h^2