You could use the difference of two squares method.
Divide both sides of the equation by 2 to get x^2 = 100
Subtract 100 from both sides to get x^2 - 100 = 0
Then factor it to get (x - 10)(x + 10) = 0
Set each factor equal to 0 and solve
x - 10 = 0
x = 10
and
x + 10 = 0
x = - 10
