x(x+6)=80

Solution for x(x+6)=80 equation:

x(x+6)=80

We move all terms to the left:

x(x+6)-(80)=0

We multiply parentheses

x^2+6x-80=0

a = 1; b = 6; c = -80;
Δ = b2-4ac
Δ = 62-4·1·(-80)
Δ = 356
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:

$\sqrt{\Delta}=\sqrt{356}=\sqrt{4*89}=\sqrt{4}*\sqrt{89}=2\sqrt{89}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(6)-2\sqrt{89}}{2*1}=\frac{-6-2\sqrt{89}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(6)+2\sqrt{89}}{2*1}=\frac{-6+2\sqrt{89}}{2}
$