28=x^2+16x

Solution for 28=x^2+16x equation:

28=x^2+16x

We move all terms to the left:

28-(x^2+16x)=0

We get rid of parentheses

-x^2-16x+28=0

We add all the numbers together, and all the variables

-1x^2-16x+28=0

a = -1; b = -16; c = +28;
Δ = b2-4ac
Δ = -162-4·(-1)·28
Δ = 368
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:

$\sqrt{\Delta}=\sqrt{368}=\sqrt{16*23}=\sqrt{16}*\sqrt{23}=4\sqrt{23}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-16)-4\sqrt{23}}{2*-1}=\frac{16-4\sqrt{23}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-16)+4\sqrt{23}}{2*-1}=\frac{16+4\sqrt{23}}{-2}
$