X^2-2x-8=10

Solution for X^2-2x-8=10 equation:

X^2-2X-8=10

We move all terms to the left:

X^2-2X-8-(10)=0

We add all the numbers together, and all the variables

X^2-2X-18=0

a = 1; b = -2; c = -18;
Δ = b2-4ac
Δ = -22-4·1·(-18)
Δ = 76
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:

$\sqrt{\Delta}=\sqrt{76}=\sqrt{4*19}=\sqrt{4}*\sqrt{19}=2\sqrt{19}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2)-2\sqrt{19}}{2*1}=\frac{2-2\sqrt{19}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+2\sqrt{19}}{2*1}=\frac{2+2\sqrt{19}}{2}
$