V=(36-2x)(28-2x)

Solution for V=(36-2x)(28-2x) equation:

=(36-2V)(28-2V)

We move all terms to the left:

-((36-2V)(28-2V))=0

We add all the numbers together, and all the variables

-((-2V+36)(-2V+28))=0

We multiply parentheses ..

-((+4V^2-56V-72V+1008))=0


We calculate terms in parentheses: -((+4V^2-56V-72V+1008)), so:

(+4V^2-56V-72V+1008)

We get rid of parentheses

4V^2-56V-72V+1008

We add all the numbers together, and all the variables

4V^2-128V+1008

Back to the equation:

-(4V^2-128V+1008)


We get rid of parentheses

-4V^2+128V-1008=0

a = -4; b = 128; c = -1008;
Δ = b2-4ac
Δ = 1282-4·(-4)·(-1008)
Δ = 256
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$V_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$V_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{256}=16$
$V_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(128)-16}{2*-4}=\frac{-144}{-8}
=+18
$
$V_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(128)+16}{2*-4}=\frac{-112}{-8}
=+14
$