对称轴x=-2设f(x)=ax²+4ax +c(x1-x2)²=(x1+x2)²-4x1x2=16 - 4c/a=8 c=2af(0)=2a=±1a=±1/2f(x)=x²/2 +2x + 1或者f(x)=-x²/2 -2x - 1