您所在的当前位置：高中数学试题 >

等差数列

> 已知各项都不相等的等差数列{a n}的前六项和为60，且a 6为a 1和a 21的等比中项．（I）求数列{a n}的通项公式a n；（II）若数列 {bn}满足bn+1-bn=an(n∈N*)，且b1=3，求数列{bn}的通项公式bn；（III）求数列 { 1 bn-n }的前n项和Tn．

问题：

发布时间：2024-09-11

已知各项都不相等的等差数列{a _n}的前六项和为60，且a ₆为a ₁和a ₂₁的等比中项．
（I）求数列{a _n}的通项公式a _n；
（II）若数列 {bn}满足bn+1-bn=an(n∈N*)，且b1=3，求数列{bn}的通项公式bn；
（III）求数列 {

1

bn-n

}的前n项和Tn．

参考答案：

提问用户：di***PDM

可能感兴趣的题目：

1 下列说法正确的是（　　） A．有公共顶点的两个角是对顶角 B．两条直线相交所成的角是对顶角 C．有公共顶点且有一条公共边的两个角是邻补角 D．两条直线相交所成的无公共边的两个角是对顶角
2 　　“五月渔郎相忆否？小楫轻舟，梦人芙蓉浦”中的“芙蓉浦”是周邦彦思乡时梦中所见。请对词中 “芙蓉浦”的梦境展开合理想象，进行生动描写，表达词人的思乡之情。（80字以内）　_______________________________________________________________
3 阅读下面一首唐诗，然后回答问题。晚春韩愈草树知春不久归，百般红紫斗芳菲。杨花榆荚无才思，唯解漫天作雪飞。（1）本诗用了拟人的修辞手法，请找出两个关键的词语进行赏析。 _________________________________________________ （2）《晚春》是韩愈诗中颇富情趣的小品，人们对诗意的理解诸说不一。请对三、四句中“杨花榆荚”的形象作分析，谈谈你的看法。 _________________________________________________
4 阅读理解。 Mobile phone has become a problem for middle schools. Some middle schools in Australia have banned students from carrying mobile phones during school hours. Mobile phone use among children has become a problem for the school this year. Several children have got mobile phones as Christmas gifts, and more students will want them. Mary Bluett, an official, said mobile phone use is a distraction to students during school hours and it also gives teachers so much trouble in their classrooms. Teachers were also saying that sometimes students might use phone messages to cheat during exams. She said some schools had tried to ban mobile phones. Some parents felt unhappy because they couldn"t get in touch with their children. Many teachers said students should not have mobile phones at school, but if there was a good reason, they could leave their phones at school office. They also said there were many reasons why the students should not have mobile phones at school; they were easy to lose and were a distraction from studies. Many people say that they understand why parents would want their children to have phones, but they think schools should let the students know when they can use their mobile phones. 1. Some middle schools in Australia have banned students from carrying mobile phones _____. A. because they are students B. when they are free C. when they are at school D. because they are children 2. We know from the passage that some children get mobile phones from _____. A. the makers and sellers B. the passers-by and strangers C. their parents and friends D. some mobile phone users 3. What does the underlined word "cheat" mean in the passage? A. 聊天 B. 核对 C. 查询 D. 作弊 4. Some parents felt unhappy because they couldn"t _____ during school hours. A. use their mobile phones B. leave their mobile phones at school office C. help the teachers with their work D. get in touch with their children
5 简述国库存款的种类。
6 影响行政组织结构与效率的决定性因素（） A 经费 B 图书资料 C 人员素质和结构 D 物资设备
7 —Sandy, our son is 9 years tomorrow. —Oh,yes.We should (应该) have a party for his ________ birthday. [ ] A. nine B. ninth C. the ninth
8 下列词语中加点的字，读音全都正确的一组是（） A．通牒（dié）埋怨（mái）罪己诏（zhào）毛骨悚然（sǒng） B．摒弃（bǐng）恢弘（hóng）炭疽热（jū）鉴往知来（jiàn） C．恸哭（tòng）斡旋（wò）露马脚（lòu）针砭时弊（biān） D．狙击（jū）喝彩（hè）拓荒者（tuò）嘉言懿行（yí）
9 动物学家用一种特殊的照相机(其镜头相当于一个凸透镜)，给体积较小的昆虫拍照，能够在照相胶片上获得昆虫清晰放大的像，那么拍照时昆虫到镜头的距离 [ ] A.小于焦距 B.大于焦距小于2倍焦距 C.等于2倍焦距 D.大于2倍焦距
10 对设计技术与工程进度的关系作分析比较，这项工作的主要时间段在( )。 A 施工准备工作阶段 B 设计工作的前期 C 招标采购阶段 D 设计工作的后期

已知各项都不相等的等差数列{a n}的前六项和为60，且a 6为a 1和a 21的等比中项． （I）求数列{a n}的通项公式a n； （II）若数列 {bn}满足bn+1-bn=an(n∈N*)，且b1=3，求数列{bn}的通项公式bn； （III）求数列 { 1 bn-n }的前n项和Tn．

可能感兴趣的题目：