Complete Set of Representatives Problems

For which exponents k is {1^k, 2^k, 3^k, 4^k, 5^k, 6^k, 7^k, 8^k, 9^k, 10^k, 11^k} a complete set of representatives modulo 11?

At this point in our course we have covered Induction, Euclid's Algorithm, Unique Factorization, Congruence, Congruence Classes, and Rings/Fields.

I have tried solving this problem several ways. I know that the set is a complete representatives if the set consists of 11 integers (which it does) and no integer in the set is congruent to any other integer in the set. So, i have set a^k=(congruent)b^k (mod 11) where a,b E Set with a>b, and then tried to use this to figure for which values of k this can be true (and then by finding that all other k make the set a complete set of representatives) but I cannot seem to find a way to solve for k.

Any help would be very much appriciated! Thanks!