In my opinion, the best way to memorize the quadratic formula is through understanding where it comes from. It is easier to start with the standard polynomial equation:
ax^2+bx+c=0
then all we need to do is solve for both x’s. That is why there is a + and a – in the quadratic formula.
divide by a.
x^2+bx/a+c/a=0
Now just Complete the square
(x-((-b +sqrt (b^2-4ac))/2a))*(x-((-b -sqrt (b^2-4ac))/2a))=0
now you can easily see that:
x= (-b +/- sqrt (b^2-4ac))/2a (Quadratic formula!)