Question

①已知f（2x)=2x+3,求f(x) ②已知g(x)=1-2x,f[g(x)]=1-x²/x²,求

Answer 1

设2x=t 则f（t）=t+3 ∴f（x）=x+3

(2)若g(x)=1-2x,f[g(x)]=(1-x^2)/x^2,则f(1/2)的值为

f[g(x) ]

=(1-x^2)/x^2

令g(x)=1/2

1-2x=1/2

2x=1/2

x=1/4

f(1/2)=(1-x^2)/x^2

令x=1/4

有:

f(1/2)=(1-(1/4)^2)/(1/4)^2

=15