This is the first time for me on symmetric functions. Let us consider the symmetric function $p_k({x_1},{x_2},...,{x_n})={x_1}^k+{x_2}^k+...+{x_n}^k$ on $GF(q)=\{0,a_1,a_2,...,a_{q-1}\}$.
I want to show that:
a) $p_{q-1}(a_1,...,a_{q-1})=-1$
b) $p_{k}(a_1,...,a_{q-1})= 0$ for all $0 < k \leq q-2$.
Some hints or procedure? $GF(q)$ is cyclic so for the first point there is some recursivity, but how can I handle this problem?