x=0,25x^2-20

Solution for x=0,25x^2-20 equation:

x=0.25x^2-20

We move all terms to the left:

x-(0.25x^2-20)=0

We get rid of parentheses

-0.25x^2+x+20=0

a = -0.25; b = 1; c = +20;
Δ = b2-4ac
Δ = 12-4·(-0.25)·20
Δ = 21
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(1)-\sqrt{21}}{2*-0.25}=\frac{-1-\sqrt{21}}{-0.5}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+\sqrt{21}}{2*-0.25}=\frac{-1+\sqrt{21}}{-0.5}
$