0=2x(x-21)

Solution for 0=2x(x-21) equation:

0=2x(x-21)

We move all terms to the left:

0-(2x(x-21))=0

We add all the numbers together, and all the variables

-(2x(x-21))=0


We calculate terms in parentheses: -(2x(x-21)), so:

2x(x-21)

We multiply parentheses

2x^2-42x

Back to the equation:

-(2x^2-42x)


We get rid of parentheses

-2x^2+42x=0

a = -2; b = 42; c = 0;
Δ = b2-4ac
Δ = 422-4·(-2)·0
Δ = 1764
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1764}=42$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(42)-42}{2*-2}=\frac{-84}{-4}
=+21
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(42)+42}{2*-2}=\frac{0}{-4}
=0
$