Step 1 :
After factoring out $ 2x^{2} $ we have:
$$ 2x^{4}-242x^{2} = 2x^{2} ( x^{2}-121 ) $$Step 2 :
Rewrite $ x^{2}-121 $ as:
$$ x^{2}-121 = (x)^2 - (11)^2 $$Now we can apply the difference of squares formula.
$$ I^2 - II^2 = (I - II)(I + II) $$After putting $ I = x $ and $ II = 11 $ , we have:
$$ x^{2}-121 = (x)^2 - (11)^2 = ( x-11 ) ( x+11 ) $$