0=x^2-20x-9900

Solution for 0=x^2-20x-9900 equation:

0=x^2-20x-9900

We move all terms to the left:

0-(x^2-20x-9900)=0

We add all the numbers together, and all the variables

-(x^2-20x-9900)=0

We get rid of parentheses

-x^2+20x+9900=0

We add all the numbers together, and all the variables

-1x^2+20x+9900=0

a = -1; b = 20; c = +9900;
Δ = b2-4ac
Δ = 202-4·(-1)·9900
Δ = 40000
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{40000}=200$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20)-200}{2*-1}=\frac{-220}{-2}
=+110
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20)+200}{2*-1}=\frac{180}{-2}
=-90
$