(5v+4)(8-v)=0

Solution for (5v+4)(8-v)=0 equation:

(5v+4)(8-v)=0

We add all the numbers together, and all the variables

(5v+4)(-1v+8)=0

We multiply parentheses ..

(-5v^2+40v-4v+32)=0

We get rid of parentheses

-5v^2+40v-4v+32=0

We add all the numbers together, and all the variables

-5v^2+36v+32=0

a = -5; b = 36; c = +32;
Δ = b2-4ac
Δ = 362-4·(-5)·32
Δ = 1936
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$v_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$v_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1936}=44$
$v_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(36)-44}{2*-5}=\frac{-80}{-10}
=+8
$
$v_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(36)+44}{2*-5}=\frac{8}{-10}
=-4/5
$