0=25x-x^2-100

Solution for 0=25x-x^2-100 equation:

0=25x-x^2-100

We move all terms to the left:

0-(25x-x^2-100)=0

We add all the numbers together, and all the variables

-(25x-x^2-100)=0

We get rid of parentheses

x^2-25x+100=0

a = 1; b = -25; c = +100;
Δ = b2-4ac
Δ = -252-4·1·100
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-25)-15}{2*1}=\frac{10}{2}
=5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-25)+15}{2*1}=\frac{40}{2}
=20
$