题目

设数列的各项都是正数，， ， . ⑴求数列的通项公式；⑵求数列的通项公式； ⑶求证： . 答案：（1）；（2） ；  （3）同解析 解析:⑴由条件得：  ∴       ∵ ∴ ∴为等比数列∴       ⑵由   得                  又   ∴                     ⑶∵            （或由即） ∴为递增数列。                             ∴从而     ∴              假定英语课上老师要求同桌之间交换修改作文，请你修改你同桌写的以下作文。文中共有10处语言错误，每句中最多有两处。每处错误仅涉及一个单词的增加、删除或修改。增加：在缺词处加一个漏字符号（∧）并在其下面写出该加的词。删除：把多余的词用斜线（＼）划掉。修改：在错的词下划一横线，并在该词下面写出修改后的词。注意：1. 每处错误及其修改均仅限一词；2. 只允许修改10处，多者（从第11处起）不计分。Many students tend to copy others’ homework while the deadline comes, as is often the case. But nowadays, more students chose to hire someone to write to homework for them. Therefore, on-line ghostwriting has emerged to meet students’ needs. In our surprise, parents make up a large part in those homework buyer.Too much homework may be main reason for ghostwriting phenomenon. Many students cannot finish their homework on time, but they do this to avoid the punishment of their teachers. Beside, poor sense of time makes this too late for students to finish homework before deadline.In my opinion, proper amount of homework and the cultivation of sense of time may help solving this problem.