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