0=-x2+8x+9

Solution for 0=-x2+8x+9 equation:

0=-x2+8x+9

We move all terms to the left:

0-(-x2+8x+9)=0

We add all the numbers together, and all the variables

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

We add all the numbers together, and all the variables

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

We get rid of parentheses

1x^2-8x-9=0

We add all the numbers together, and all the variables

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