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

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

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

We multiply parentheses ..

(-20x^2-15x-16x-12)=0

We get rid of parentheses

-20x^2-15x-16x-12=0

We add all the numbers together, and all the variables

-20x^2-31x-12=0

a = -20; b = -31; c = -12;
Δ = b2-4ac
Δ = -312-4·(-20)·(-12)
Δ = 1
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1}=1$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-31)-1}{2*-20}=\frac{30}{-40}
=-3/4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-31)+1}{2*-20}=\frac{32}{-40}
=-4/5
$