28=4(x+2)x

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

28=4(x+2)x

We move all terms to the left:

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


We calculate terms in parentheses: -(4(x+2)x), so:

4(x+2)x

We multiply parentheses

4x^2+8x

Back to the equation:

-(4x^2+8x)


We get rid of 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}
$