15x+3x(8+x)=0

Solution for 15x+3x(8+x)=0 equation:

15x+3x(8+x)=0

We add all the numbers together, and all the variables

15x+3x(x+8)=0

We multiply parentheses

3x^2+15x+24x=0

We add all the numbers together, and all the variables

3x^2+39x=0

a = 3; b = 39; c = 0;
Δ = b2-4ac
Δ = 392-4·3·0
Δ = 1521
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1521}=39$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(39)-39}{2*3}=\frac{-78}{6}
=-13
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(39)+39}{2*3}=\frac{0}{6}
=0
$