(4-v)(5v-7)=0

Solution for (4-v)(5v-7)=0 equation:

(4-v)(5v-7)=0

We add all the numbers together, and all the variables

(-1v+4)(5v-7)=0

We multiply parentheses ..

(-5v^2+7v+20v-28)=0

We get rid of parentheses

-5v^2+7v+20v-28=0

We add all the numbers together, and all the variables

-5v^2+27v-28=0

a = -5; b = 27; c = -28;
Δ = b2-4ac
Δ = 272-4·(-5)·(-28)
Δ = 169
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$v_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$v_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{169}=13$
$v_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(27)-13}{2*-5}=\frac{-40}{-10}
=+4
$
$v_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(27)+13}{2*-5}=\frac{-14}{-10}
=1+2/5
$