y=ax²+bx+c=a(x²+bx/a)+c=a[x²+bx/a+(b/2a)²-(b/2a)²]+c=a[x²+bx/a+b²/(4a²)-a[b²/(4a²)]+c=a[x+b/(2a)]²+c-b²/(4a)=a[x+b/(2a)]²+(4ac-b²)...