(x-1)(2x)=28

Solution for (x-1)(2x)=28 equation:

(x-1)(2x)=28

We move all terms to the left:

(x-1)(2x)-(28)=0

We multiply parentheses

2x^2-2x-28=0

a = 2; b = -2; c = -28;
Δ = b2-4ac
Δ = -22-4·2·(-28)
Δ = 228
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:

$\sqrt{\Delta}=\sqrt{228}=\sqrt{4*57}=\sqrt{4}*\sqrt{57}=2\sqrt{57}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2)-2\sqrt{57}}{2*2}=\frac{2-2\sqrt{57}}{4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+2\sqrt{57}}{2*2}=\frac{2+2\sqrt{57}}{4}
$