4x(x-2)=28

Solution for 4x(x-2)=28 equation:

4x(x-2)=28

We move all terms to the left:

4x(x-2)-(28)=0

We multiply parentheses

4x^2-8x-28=0

a = 4; b = -8; c = -28;
Δ = b2-4ac
Δ = -82-4·4·(-28)
Δ = 512
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:

$\sqrt{\Delta}=\sqrt{512}=\sqrt{256*2}=\sqrt{256}*\sqrt{2}=16\sqrt{2}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8)-16\sqrt{2}}{2*4}=\frac{8-16\sqrt{2}}{8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8)+16\sqrt{2}}{2*4}=\frac{8+16\sqrt{2}}{8}
$