x2+2x=255

Solution for x2+2x=255 equation:

x2+2x=255

We move all terms to the left:

x2+2x-(255)=0

We add all the numbers together, and all the variables

x^2+2x-255=0

a = 1; b = 2; c = -255;
Δ = b2-4ac
Δ = 22-4·1·(-255)
Δ = 1024
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1024}=32$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2)-32}{2*1}=\frac{-34}{2}
=-17
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2)+32}{2*1}=\frac{30}{2}
=15
$