x^2-2x-7920=0

Solution for x^2-2x-7920=0 equation:

x^2-2x-7920=0

a = 1; b = -2; c = -7920;
Δ = b2-4ac
Δ = -22-4·1·(-7920)
Δ = 31684
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{31684}=178$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2)-178}{2*1}=\frac{-176}{2}
=-88
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+178}{2*1}=\frac{180}{2}
=90
$