解 :f(x)+2f(-x)=3x^2+4x+4 (1)
用-x代替x得
f(-x)+2f(x) =3x^2-4x+4 (2)
(2)×2-(1)得
3f(x)=3x^2-12x+4
∴f(x)=x^2 -4x +4/3