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

Solution for (9-x)(9+x)=0 equation:

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

We add all the numbers together, and all the variables

(-1x+9)(x+9)=0

We multiply parentheses ..

(-1x^2-9x+9x+81)=0

We get rid of parentheses

-1x^2-9x+9x+81=0

We add all the numbers together, and all the variables

-1x^2+81=0

a = -1; b = 0; c = +81;
Δ = b2-4ac
Δ = 02-4·(-1)·81
Δ = 324
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{324}=18$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-18}{2*-1}=\frac{-18}{-2}
=+9
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+18}{2*-1}=\frac{18}{-2}
=-9
$