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