ax^2+bx+c=0
1) x1+x2=-b/a
2) x1*x2=c/a

ax^3+bx^2+cx+d=0
1) x1+x2+x3=-b/a
2) x1x2x3=-d/a
3) x1x2+x1x3+x2x3=c/a

ax^4+bx^3+cx^2+dx+e=0
1) x1+x2+x3+x4=-b/a
2) x1x2x3x4=e/a
3) x1x2+x1x3+x1x4+x2x3+x2x4+x3x4=c/a
4) x1x2x3+x1x2x4+x2x3x4+x1x3x4=-d/a

curio: x1^3+x2^3=(x1+x2)^3-3x1x2(x1+x2)