(2x)(2x-5)=56

Solution for (2x)(2x-5)=56 equation:

(2x)(2x-5)=56

We move all terms to the left:

(2x)(2x-5)-(56)=0

We multiply parentheses

4x^2-10x-56=0

a = 4; b = -10; c = -56;
Δ = b2-4ac
Δ = -102-4·4·(-56)
Δ = 996
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:

$\sqrt{\Delta}=\sqrt{996}=\sqrt{4*249}=\sqrt{4}*\sqrt{249}=2\sqrt{249}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-10)-2\sqrt{249}}{2*4}=\frac{10-2\sqrt{249}}{8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-10)+2\sqrt{249}}{2*4}=\frac{10+2\sqrt{249}}{8}
$