Please help with questions 3, 4, and 5.

1 3) For which a does n(In n) a converge? Justify your answer. n=2 4) Determine whether the series converges absolutely, conditionally, or not at all (Justify your answer): cos n 2n n=1 5) Determine convergence or divergence using any method covered so far (up to section 10.5.) Justify your answer: OC 3 n= n