390=2x*(x-2)

Solution for 390=2x*(x-2) equation:

390=2x(x-2)

We move all terms to the left:

390-(2x(x-2))=0


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

2x(x-2)

We multiply parentheses

2x^2-4x

Back to the equation:

-(2x^2-4x)


We get rid of parentheses

-2x^2+4x+390=0

a = -2; b = 4; c = +390;
Δ = b2-4ac
Δ = 42-4·(-2)·390
Δ = 3136
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3136}=56$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(4)-56}{2*-2}=\frac{-60}{-4}
=+15
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(4)+56}{2*-2}=\frac{52}{-4}
=-13
$