x^2=20^2+21^2

Solution for x^2=20^2+21^2 equation:

x^2=20^2+21^2

We move all terms to the left:

x^2-(20^2+21^2)=0

We add all the numbers together, and all the variables

x^2-841=0

a = 1; b = 0; c = -841;
Δ = b2-4ac
Δ = 02-4·1·(-841)
Δ = 3364
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3364}=58$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-58}{2*1}=\frac{-58}{2}
=-29
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+58}{2*1}=\frac{58}{2}
=29
$