784=2x*x

Solution for 784=2x*x equation:

784=2x*x

We move all terms to the left:

784-(2x*x)=0

We add all the numbers together, and all the variables

-(+2x*x)+784=0

We get rid of parentheses

-2x*x+784=0

Wy multiply elements

-2x^2+784=0

a = -2; b = 0; c = +784;
Δ = b2-4ac
Δ = 02-4·(-2)·784
Δ = 6272
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:

$\sqrt{\Delta}=\sqrt{6272}=\sqrt{3136*2}=\sqrt{3136}*\sqrt{2}=56\sqrt{2}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-56\sqrt{2}}{2*-2}=\frac{0-56\sqrt{2}}{-4}
=-\frac{56\sqrt{2}}{-4}
=-\frac{14\sqrt{2}}{-1}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+56\sqrt{2}}{2*-2}=\frac{0+56\sqrt{2}}{-4}
=\frac{56\sqrt{2}}{-4}
=\frac{14\sqrt{2}}{-1}
$