(x-2)(2x)=40

Solution for (x-2)(2x)=40 equation:

(x-2)(2x)=40

We move all terms to the left:

(x-2)(2x)-(40)=0

We multiply parentheses

2x^2-4x-40=0

a = 2; b = -4; c = -40;
Δ = b2-4ac
Δ = -42-4·2·(-40)
Δ = 336
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:

$\sqrt{\Delta}=\sqrt{336}=\sqrt{16*21}=\sqrt{16}*\sqrt{21}=4\sqrt{21}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-4)-4\sqrt{21}}{2*2}=\frac{4-4\sqrt{21}}{4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4)+4\sqrt{21}}{2*2}=\frac{4+4\sqrt{21}}{4}
$