20=5*x^2

Solution for 20=5*x^2 equation:

20=5x^2

We move all terms to the left:

20-(5x^2)=0

a = -5; b = 0; c = +20;
Δ = b2-4ac
Δ = 02-4·(-5)·20
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-20}{2*-5}=\frac{-20}{-10}
=+2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+20}{2*-5}=\frac{20}{-10}
=-2
$