For any quadratic equation $ax^2+bx+c$, $x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}$
Proof:
$ax^2+bx+c$
$ax^2+bx=-c$
$x^2+\frac{b}{a}x=-\frac{c}{a}$
$x^2+\frac{b}{a}x+\frac{b^2}{4a^2}=\frac{b^2}{4a^2}-\frac{c}{a}$
$(x+\frac{b}{2a})^2=\frac{b^2}{4a^2}-\frac{c}{a}$
$(x+\frac{b}{2a})^2=\frac{b^2}{4a^2}-\frac{4ac}{4a^2}$
$(x+\frac{b}{2a})^2=\frac{b^2-4ac}{4a^2}$
$x+\frac{b}{2a}=\pm\frac{\sqrt{b^2-4ac}}{\sqrt{4a^2}}$
$x+\frac{b}{2a}=\pm\frac{\sqrt{b^2-4ac}}{2a}$
$x=-\frac{b}{2a}\pm\frac{\sqrt{b^2-4ac}}{2a}$
$x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}$
QED