X2+2x=104

Solution for X2+2x=104 equation:

X2+2X=104

We move all terms to the left:

X2+2X-(104)=0

We add all the numbers together, and all the variables

X^2+2X-104=0

a = 1; b = 2; c = -104;
Δ = b2-4ac
Δ = 22-4·1·(-104)
Δ = 420
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{420}=\sqrt{4*105}=\sqrt{4}*\sqrt{105}=2\sqrt{105}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2)-2\sqrt{105}}{2*1}=\frac{-2-2\sqrt{105}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2)+2\sqrt{105}}{2*1}=\frac{-2+2\sqrt{105}}{2}
$