(2x)(x-3)=80

Solution for (2x)(x-3)=80 equation:

(2x)(x-3)=80

We move all terms to the left:

(2x)(x-3)-(80)=0

We multiply parentheses

2x^2-6x-80=0

a = 2; b = -6; c = -80;
Δ = b2-4ac
Δ = -62-4·2·(-80)
Δ = 676
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{676}=26$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-6)-26}{2*2}=\frac{-20}{4}
=-5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-6)+26}{2*2}=\frac{32}{4}
=8
$