令3x-2=t
x=(t+2)/3
f(t)=3*[(t+2)/3]^2-2(t+2)/3+1
=(t+2)^2/3-(2t+4)/3+1
=(t^2+4t+4-2t-4+3)/3
=(t^2+2t+3)/3
即f(x)=(x^2+2x+3)/3