法一：换元法令t=2x+1,则x=(t-1)/2f(t)=[(t-1)/2]²+4×(t-1)/2=(t-1)²/4+2(t-1)=t²/4+3t/2-7/4所以f(x)=x²/4+3x/2-7/4 法二：配凑法f(2x+1)=x²+4x=1/4 (4x²+16x)=1/4 (4x²+4x+1+...