(X+8)x=128

Solution for (X+8)x=128 equation:

(X+8)X=128

We move all terms to the left:

(X+8)X-(128)=0

We multiply parentheses

X^2+8X-128=0

a = 1; b = 8; c = -128;
Δ = b2-4ac
Δ = 82-4·1·(-128)
Δ = 576
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{576}=24$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(8)-24}{2*1}=\frac{-32}{2}
=-16
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(8)+24}{2*1}=\frac{16}{2}
=8
$