X+x1+x2=423

Solution for X+x1+x2=423 equation:

X+X1+X2=423

We move all terms to the left:

X+X1+X2-(423)=0

We add all the numbers together, and all the variables

X^2+2X-423=0

a = 1; b = 2; c = -423;
Δ = b2-4ac
Δ = 22-4·1·(-423)
Δ = 1696
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:

$\sqrt{\Delta}=\sqrt{1696}=\sqrt{16*106}=\sqrt{16}*\sqrt{106}=4\sqrt{106}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2)-4\sqrt{106}}{2*1}=\frac{-2-4\sqrt{106}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2)+4\sqrt{106}}{2*1}=\frac{-2+4\sqrt{106}}{2}
$