(20+x)*x=224

Solution for (20+x)*x=224 equation:

(20+x)*x=224

We move all terms to the left:

(20+x)*x-(224)=0

We add all the numbers together, and all the variables

(x+20)*x-224=0

We multiply parentheses

x^2+20x-224=0

a = 1; b = 20; c = -224;
Δ = b2-4ac
Δ = 202-4·1·(-224)
Δ = 1296
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1296}=36$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20)-36}{2*1}=\frac{-56}{2}
=-28
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20)+36}{2*1}=\frac{16}{2}
=8
$