设y=ax^2+bx+c,与x轴交点为(x1,0),(x2,0)由题意(1)a-b+c=-1(2)-b/2a=-2(3)| x1-x2 | =2√2(4) x1+x2=-b/a,x1*x2=c/a由（2）得 b=4a 代入（1）得c=3a-1 (5)着重看（3）| x1-x2 |=√(x1-x2)^2=√[(x1+x2)^2-4x1*x2]=2...