See if you can figure out what all this math stuff means:
$$ax^2+bx+c=0$$
$$ax^2+bx=-c$$
$$x^2+\frac{b}{a}x=-\frac{c}{a}$$
$$ax^2+\frac{b}{a}x+(\frac{b}{2a})^2=-\frac{c}{a}+\frac{b^2}{4a^2}$$
What do you think these lines are doing?
Fantastic! Your answer is correct. Write it in your notes.