720=(20+2x)(16+2x)

Solution for 720=(20+2x)(16+2x) equation:

720=(20+2x)(16+2x)

We move all terms to the left:

720-((20+2x)(16+2x))=0

We add all the numbers together, and all the variables

-((2x+20)(2x+16))+720=0

We multiply parentheses ..

-((+4x^2+32x+40x+320))+720=0


We calculate terms in parentheses: -((+4x^2+32x+40x+320)), so:

(+4x^2+32x+40x+320)

We get rid of parentheses

4x^2+32x+40x+320

We add all the numbers together, and all the variables

4x^2+72x+320

Back to the equation:

-(4x^2+72x+320)


We get rid of parentheses

-4x^2-72x-320+720=0

We add all the numbers together, and all the variables

-4x^2-72x+400=0

a = -4; b = -72; c = +400;
Δ = b2-4ac
Δ = -722-4·(-4)·400
Δ = 11584
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{11584}=\sqrt{64*181}=\sqrt{64}*\sqrt{181}=8\sqrt{181}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-72)-8\sqrt{181}}{2*-4}=\frac{72-8\sqrt{181}}{-8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-72)+8\sqrt{181}}{2*-4}=\frac{72+8\sqrt{181}}{-8}
$