Step 1 :
After factoring out $ 3 $ we have:
$$ 48x^{8}-27 = 3 ( 16x^{8}-9 ) $$Step 2 :
Rewrite $ 16x^{8}-9 $ as:
$$ 16x^{8}-9 = (4x^{4})^2 - (3)^2 $$Now we can apply the difference of squares formula.
$$ I^2 - II^2 = (I - II)(I + II) $$After putting $ I = 4x^{4} $ and $ II = 3 $ , we have:
$$ 16x^{8}-9 = (4x^{4})^2 - (3)^2 = ( 4x^{4}-3 ) ( 4x^{4}+3 ) $$