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