In any sequence of n nonzero numbers, a pair of consecutive terms with opposite signs represents a sign change. For example, the sequence –2, 3, –4, 5 has three sign changes. Does the sequence of nonzero numbers s_1, s_2, s_3, - , s_n have an even number of sign changes?
1.s_k= (-1)^{k} for all positive integers k from 1 to n.
2.n is odd.