i) Prove that there exists N(which is belongs to Natural numbers) such that for any n (Natural numbers) if n >N then 0≦an^2≦an. 20 points
ii) Prove that (∞Σn=1)an^2 converges.
b) If (∞Σn=1)an^2 converges is it necessary true that (∞Σn=1)an converges?
Give reason to justify your assertion.
只需答part b，a part已解~
更新1:
問：你係 part a solved 還是 part b solved? 我只看此問題所以以為 part a solved，但係以後睇番另一題，你係問 part b wor. 覆：這一條題目有part a 和 b，我已經識做part a ，在這裡只是想請教各位part b點做，故答part b 已經足夠(post埋part a出來是因為part b 可能要用part a results，thz)
