(9+x)(9-x)=17

Solution for (9+x)(9-x)=17 equation:

(9+x)(9-x)=17

We move all terms to the left:

(9+x)(9-x)-(17)=0

We add all the numbers together, and all the variables

(x+9)(-1x+9)-17=0

We multiply parentheses ..

(-1x^2+9x-9x+81)-17=0

We get rid of parentheses

-1x^2+9x-9x+81-17=0

We add all the numbers together, and all the variables

-1x^2+64=0

a = -1; b = 0; c = +64;
Δ = b2-4ac
Δ = 02-4·(-1)·64
Δ = 256
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{256}=16$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-16}{2*-1}=\frac{-16}{-2}
=+8
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+16}{2*-1}=\frac{16}{-2}
=-8
$