ax^2+bx+c=0
a(x^2+bx/a)=-c
a(x^2+bx/a+b^2/4a^2)=b^2/4a-c=(b^2-4ac)/4a
(x+b/2a)^2=(b^2-4ac)/4a^2
x+b/2a=±√(b^2-4ac)/2a
x=-b/2a±√(b^2-4ac)/2a=[-b±√(b^2-4ac)]/2a