100=x(20-x)

Solution for 100=x(20-x) equation:

100=x(20-x)

We move all terms to the left:

100-(x(20-x))=0

We add all the numbers together, and all the variables

-(x(-1x+20))+100=0


We calculate terms in parentheses: -(x(-1x+20)), so:

x(-1x+20)

We multiply parentheses

-1x^2+20x

Back to the equation:

-(-1x^2+20x)


We get rid of parentheses

1x^2-20x+100=0

We add all the numbers together, and all the variables

x^2-20x+100=0

a = 1; b = -20; c = +100;
Δ = b2-4ac
Δ = -202-4·1·100
Δ = 0
Delta is equal to zero, so there is only one solution to the equation

                              Stosujemy wzór:
$x=\frac{-b}{2a}=\frac{20}{2}=10$