令x+1=t,则x=t-1f(t)=3(t-1)+2=3t-1所以f(x)=3x-1
设t =x+1,则x=t-1.的f(t)=3*(t-1)+2=3t-1.所以f(x)=3x-1
f(x+1)=3x+2f(x)=3(x-1)+2 =3x-3+2 =3x-1
f(x+1)=3x+2 =3(x+1)-1所以f(x)=3x-1