For a set with 10 elements, there are 2^10=1024 subsets (S_1, S_2, S_3, ..., S_1024). Obviously, 0=Suppose sum(S_N)=sum(S_M). If S_N and S_M are othogonal (no common elements), we proved the problem. If they are not, remove the common elements.www.ddhw.com