Question

已知f(3x-1)=x²+2x+4,则f(x)=?

Answer 1

令3x-1=t,则x=(t+1)/3,于是

f(t)=[(t+1)/3]²+2*(t+1)/3+4

=(t²+2t+1)/9+(2t+2)/3+4

=(t²+2t+1+6t+6+36)/9

=(t²+8t+43)/9

所以

f(x)=(x²+8x+43)/9