X2+2x-1=125

Solution for X2+2x-1=125 equation:

X2+2X-1=125

We move all terms to the left:

X2+2X-1-(125)=0

We add all the numbers together, and all the variables

X^2+2X-126=0

a = 1; b = 2; c = -126;
Δ = b2-4ac
Δ = 22-4·1·(-126)
Δ = 508
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:

$\sqrt{\Delta}=\sqrt{508}=\sqrt{4*127}=\sqrt{4}*\sqrt{127}=2\sqrt{127}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2)-2\sqrt{127}}{2*1}=\frac{-2-2\sqrt{127}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2)+2\sqrt{127}}{2*1}=\frac{-2+2\sqrt{127}}{2}
$