3(2x-5)(x+4)=0

Solution for 3(2x-5)(x+4)=0 equation:

3(2x-5)(x+4)=0

We multiply parentheses ..

3(+2x^2+8x-5x-20)=0

We multiply parentheses

6x^2+24x-15x-60=0

We add all the numbers together, and all the variables

6x^2+9x-60=0

a = 6; b = 9; c = -60;
Δ = b2-4ac
Δ = 92-4·6·(-60)
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{-(9)-39}{2*6}=\frac{-48}{12}
=-4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+39}{2*6}=\frac{30}{12}
=2+1/2
$