Answer
$$0=x^2-20$$
Work Step by Step
To write a quadratic equation with the given values as solutions, we find the corresponding factors. We then FOIL out the factors to find the original quadratic equation:
$$ 0=\left(x-2\sqrt{5}\right)\left(x+2\sqrt{5}\right)\\ 0=x^2-\left(2\sqrt{5}\right)^2\\ 0=x^2-20$$