# How do you solve x^2-20=0 using the quadratic formula?

Substitute the variables for the numbers in the equation to get your answer, $\frac{\pm 4 \sqrt{5}}{2}$.
The quadratic formula is this: $\frac{- b \pm \sqrt{{b}^{2} - 4 a c}}{2 a}$. In the case of our equation, a=1, b=0, and c=-20. The equation now looks like this: $\frac{- 0 \pm \sqrt{{0}^{2} - 4 \left(1\right) \left(- 20\right)}}{2 \left(1\right)}$. We now simplify the equation to get $\frac{\pm \sqrt{80}}{2}$. 80 is not a square root, but we can simplify this even further. 16 is a square root and a factor of 80. We now get $\frac{\pm 4 \sqrt{5}}{2}$. This is our answer.