15^2+20^2=x^2

Solution for 15^2+20^2=x^2 equation:

15^2+20^2=x^2

We move all terms to the left:

15^2+20^2-(x^2)=0

We add all the numbers together, and all the variables

-1x^2+625=0

a = -1; b = 0; c = +625;
Δ = b2-4ac
Δ = 02-4·(-1)·625
Δ = 2500
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2500}=50$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-50}{2*-1}=\frac{-50}{-2}
=+25
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+50}{2*-1}=\frac{50}{-2}
=-25
$