數學興趣題（證明）

Prove that the degree of the general form of the series

1k + 2k + 3k + …… + nk is k + 1.


Also, prove that the degree of the general form of the series

ak + (a + d)k + (a + 2d)k + …… + (a + (n - 1)d)k is also k + 1.