-3x(x+4)-8=3x+4

Solution for -3x(x+4)-8=3x+4 equation:

-3x(x+4)-8=3x+4

We move all terms to the left:

-3x(x+4)-8-(3x+4)=0

We multiply parentheses

-3x^2-12x-(3x+4)-8=0

We get rid of parentheses

-3x^2-12x-3x-4-8=0

We add all the numbers together, and all the variables

-3x^2-15x-12=0

a = -3; b = -15; c = -12;
Δ = b2-4ac
Δ = -152-4·(-3)·(-12)
Δ = 81
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{81}=9$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-9}{2*-3}=\frac{6}{-6}
=-1
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+9}{2*-3}=\frac{24}{-6}
=-4
$