一元二次方程：ax^2+bx+c=a(x-x1)(x-x2)=a[x^2-(x1+x2)x+x1x2],比较系数有：x1+x2=-b/a,x1x2=c/a一元三次方程：ax^3+bx^2+cx+d=a(x-x1)(x-x2)(x-x3)=a[ x^3-(x1+x2+x3)x^2+(x1x2+x1x3+x2x3)x-x1x2x3]比较系数有：x1+...