Formula of the difference of powers.?

Question

Which is the formula of the difference of powers for:
a^n - b^n (in my case, b=1, so b^n=1)
Please give me the general formula.

Answer 1

(a-b)*(a^(n-1)+b*a(n-2)+b^2*a(n-3)......+b^(n-1))