0=x^2-8x-9

Solution for 0=x^2-8x-9 equation:

0=x^2-8x-9

We move all terms to the left:

0-(x^2-8x-9)=0

We add all the numbers together, and all the variables

-(x^2-8x-9)=0

We get rid of parentheses

-x^2+8x+9=0

We add all the numbers together, and all the variables

-1x^2+8x+9=0

a = -1; b = 8; c = +9;
Δ = b2-4ac
Δ = 82-4·(-1)·9
Δ = 100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{100}=10$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(8)-10}{2*-1}=\frac{-18}{-2}
=+9
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(8)+10}{2*-1}=\frac{2}{-2}
=-1
$