y=x/(x+2)
y(x+2)=x
xy+2y=x
x-xy=2y
(1-y)x=2y
x=2y/(1-y)
∴反函数是
y=2x/(1-x)定义域y=x/(x+2)=(x+2-2)/(x+2)=1-2/(x+2)y≠1所以函数y=2x/(1-x) 的定义域是x∈R且x≠1