i know the equation of $\displaystyle x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$ to find if at all where a function crosses the x axis but i also found you can just use $\displaystyle x = \frac{-b}{2a}$ which i really dont understand as were does the $\displaystyle \sqrt{b^2 - 4ac}$ go?