x²+px+q=x²+px+(p/2)²-(p/2)²+q=(x+(p/2))²-(p/2)²+q=0
(x+(p/2))²=(p/2)²-q>0
(x+(p/2))=±√[(p/2)²-q]
x=-(p/2)±√[(p/2)²-q]