[u(x)/v(x)]'={u(x)·[1/v(x)]}'(乘积求导)=u(x)'·[1/v(x)]+u(x)·[1/v(x)]' ([1/v(x)]'用复合函数求导,f(x)=1/x,1/v(x)=f[v(x)])=u(x)'·[1/v(x)]+u(x)·[v(x)']/[v(x)·v(x)](通分,分母变成[v(x)·v(x)])=[u(x)'·v(x)+u(x)·v(x)']/[v(x)·v(x)]