X2-8x=128

Solution for X2-8x=128 equation:

X2-8X=128

We move all terms to the left:

X2-8X-(128)=0

We add all the numbers together, and all the variables

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