Some quadratics factorise, but many do not. The quadratic formula works for any quadratic equation, even when the answers are awkward decimals or surds.

Before using it, rearrange into standard form

$$a{x}^2+bx+c=0$$

where $a$, $b$, and $c$ are the coefficients and $a\ne 0$. The biggest trap is signs, so only identify $a$, $b$, and $c$ after rearranging.

The formula is

$$x=\frac{-b\pm \sqrt{b^2-4ac}}{2a}$$

The $\pm$ means you should check a plus answer and a minus answer.