y=f(x)=1-√(x+2),的定义域为：x≥-2,值域为：y≤1
则
1-y=√(x+2)
(1-y)²=x+2
=>x=(1-y)²-2=y²-2y-1
=>f(x)=1-√x+2 的反函数y=f^(-1)(x)=y²-2y-1 ,(x≤1)