3.5=-2x^2-6x

Solution for 3.5=-2x^2-6x equation:

3.5=-2x^2-6x

We move all terms to the left:

3.5-(-2x^2-6x)=0

We get rid of parentheses

2x^2+6x+3.5=0

a = 2; b = 6; c = +3.5;
Δ = b2-4ac
Δ = 62-4·2·3.5
Δ = 8
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:

$\sqrt{\Delta}=\sqrt{8}=\sqrt{4*2}=\sqrt{4}*\sqrt{2}=2\sqrt{2}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(6)-2\sqrt{2}}{2*2}=\frac{-6-2\sqrt{2}}{4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(6)+2\sqrt{2}}{2*2}=\frac{-6+2\sqrt{2}}{4}
$