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