(a+9)(-2a-2)=0

Solution for (a+9)(-2a-2)=0 equation:

(a+9)(-2a-2)=0

We multiply parentheses ..

(-2a^2-2a-18a-18)=0

We get rid of parentheses

-2a^2-2a-18a-18=0

We add all the numbers together, and all the variables

-2a^2-20a-18=0

a = -2; b = -20; c = -18;
Δ = b2-4ac
Δ = -202-4·(-2)·(-18)
Δ = 256
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{256}=16$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-16}{2*-2}=\frac{4}{-4}
=-1
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+16}{2*-2}=\frac{36}{-4}
=-9
$