Rewrite $ -64r^{2}+1 $ as:
$$ -64r^{2}+1 = 1 -64x^2 = (1)^2 - (8r)^2 $$Now we can apply the difference of squares formula.
$$ I^2 - II^2 = (I - II)(I + II) $$After putting $ I = 1 $ and $ II = 8r $ , we have:
$$ -64r^{2}+1 = (1)^2 - (8r)^2 = ( -8r+1 ) ( 8r+1 ) $$