x^2-20x-780=0

Solution for x^2-20x-780=0 equation:

x^2-20x-780=0

a = 1; b = -20; c = -780;
Δ = b2-4ac
Δ = -202-4·1·(-780)
Δ = 3520
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:

$\sqrt{\Delta}=\sqrt{3520}=\sqrt{64*55}=\sqrt{64}*\sqrt{55}=8\sqrt{55}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-8\sqrt{55}}{2*1}=\frac{20-8\sqrt{55}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+8\sqrt{55}}{2*1}=\frac{20+8\sqrt{55}}{2}
$