25=2x*(20-x)

Solution for 25=2x*(20-x) equation:

25=2x(20-x)

We move all terms to the left:

25-(2x(20-x))=0

We add all the numbers together, and all the variables

-(2x(-1x+20))+25=0


We calculate terms in parentheses: -(2x(-1x+20)), so:

2x(-1x+20)

We multiply parentheses

-2x^2+40x

Back to the equation:

-(-2x^2+40x)


We get rid of parentheses

2x^2-40x+25=0

a = 2; b = -40; c = +25;
Δ = b2-4ac
Δ = -402-4·2·25
Δ = 1400
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:

$\sqrt{\Delta}=\sqrt{1400}=\sqrt{100*14}=\sqrt{100}*\sqrt{14}=10\sqrt{14}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-40)-10\sqrt{14}}{2*2}=\frac{40-10\sqrt{14}}{4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-40)+10\sqrt{14}}{2*2}=\frac{40+10\sqrt{14}}{4}
$