x^2+bx/a+c/a=0，

To move an item, you must:

x^2+bx/a=-c/a，

Add the square of half of the primary coefficient b/a to both sides of the equation, that is, add b 2/4a 2 to both sides of the equation, and get (formula).

x^2+bx/a+b^2/4a^2=b^2/4a^2-c/a，

That is, (x+b/2a) 2 = (b 2-4ac)/4a.

X+b/2a = [√ (b 2-4ac)]/2a。 (√ stands for root number):

x=[-b √(b^2-4ac)]/2a.