Question

函数f(x)=

2x-4

(x≥4)的反函数为（　　）

A．f-1(x)= 1 2 x2+2(x≥0)	B．f-1(x)= 1 2 x2+2(x≥2)
C．f-1(x)= 1 2 x2+4(x≥0)	D．f-1(x)= 1 2 x2+4(x≥2)

Answer 1

f(x)=

2x-4

(x≥4)?y≥2，f-1(x)=

1

2

x2+2，x≥2，
逐一验证，知B正确．
故选B．