(-3x-20)(x+1)=0

Solution for (-3x-20)(x+1)=0 equation:

(-3x-20)(x+1)=0

We multiply parentheses ..

(-3x^2-3x-20x-20)=0

We get rid of parentheses

-3x^2-3x-20x-20=0

We add all the numbers together, and all the variables

-3x^2-23x-20=0

a = -3; b = -23; c = -20;
Δ = b2-4ac
Δ = -232-4·(-3)·(-20)
Δ = 289
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{289}=17$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-23)-17}{2*-3}=\frac{6}{-6}
=-1
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-23)+17}{2*-3}=\frac{40}{-6}
=-6+2/3
$