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