Step 1 :
After factoring out $ 2x^{2} $ we have:
$$ 50x^{10}-18x^{2} = 2x^{2} ( 25x^{8}-9 ) $$Step 2 :
Rewrite $ 25x^{8}-9 $ as:
$$ 25x^{8}-9 = (5x^{4})^2 - (3)^2 $$Now we can apply the difference of squares formula.
$$ I^2 - II^2 = (I - II)(I + II) $$After putting $ I = 5x^{4} $ and $ II = 3 $ , we have:
$$ 25x^{8}-9 = (5x^{4})^2 - (3)^2 = ( 5x^{4}-3 ) ( 5x^{4}+3 ) $$