3(x+5)(x+8)=0

Solution for 3(x+5)(x+8)=0 equation:

3(x+5)(x+8)=0

We multiply parentheses ..

3(+x^2+8x+5x+40)=0

We multiply parentheses

3x^2+24x+15x+120=0

We add all the numbers together, and all the variables

3x^2+39x+120=0

a = 3; b = 39; c = +120;
Δ = b2-4ac
Δ = 392-4·3·120
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{-(39)-9}{2*3}=\frac{-48}{6}
=-8
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(39)+9}{2*3}=\frac{-30}{6}
=-5
$