28=-2x^2-18x

Solution for 28=-2x^2-18x equation:

28=-2x^2-18x

We move all terms to the left:

28-(-2x^2-18x)=0

We get rid of parentheses

2x^2+18x+28=0

a = 2; b = 18; c = +28;
Δ = b2-4ac
Δ = 182-4·2·28
Δ = 100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{100}=10$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(18)-10}{2*2}=\frac{-28}{4}
=-7
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(18)+10}{2*2}=\frac{-8}{4}
=-2
$