x(x-16)-56=0

Solution for x(x-16)-56=0 equation:

x(x-16)-56=0

We multiply parentheses

x^2-16x-56=0

a = 1; b = -16; c = -56;
Δ = b2-4ac
Δ = -162-4·1·(-56)
Δ = 480
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:

$\sqrt{\Delta}=\sqrt{480}=\sqrt{16*30}=\sqrt{16}*\sqrt{30}=4\sqrt{30}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-16)-4\sqrt{30}}{2*1}=\frac{16-4\sqrt{30}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-16)+4\sqrt{30}}{2*1}=\frac{16+4\sqrt{30}}{2}
$