数列的前项和记为,. (Ⅰ)求的通项公式; (Ⅱ)等差数列的各项为正,其前项和为且,又成等比数列. (1)求的通项公式; (2)求证:当时,. 答案:解:(Ⅰ)由,得 ,两式相减得 , 所以 -------------------------------------2分 所以 -------------------------------------3分 又所以, 从而 ---------------------------------5分 而,不符合上式, 所以 He coughed day and night.His wife asked him smoking.A. giving up B. going on C. to give up D. to go on