16. Find a formula for the partial sum S/N of (-1)^-1 and show that the series diverges. n=1 In Exercises 17-22, use the nth Term Divergence Test (Theorem 4) to prove that the following series diverge. 17. n=1 n 10n+12 18. 19. n=1 10 8 - 1 2 n n2 +1 + + 34 23 20. (-1)" n n=1 21.cos 1 2 + cos 12 1 + cos +