2022 英语周报 高中英语总复习八答案

19.解:(1)由号 =1,得23.=a a当n=1时,251=a a1,则a1=1或a1=0(舍(1分)a2 ana2-1 当n≥2时,an=S-S-1=即(an an-1)(an-an-1-1)=0,因为数列{an}各项均为正数,所以an an-1≠0,an-an-1-1=0,即an-an-1=1,数列{an}是首项为a1=1,公差d=1的等差数列,(5分所以数列{an}的通项公式an=n(6分)(2)由(1)知b.=n·2",T。=2 2·22 3·23 … n·2,①2T=22 2·23 3·24 … n·2… 1,②(10分)①一②得-T.=2 22 2 … 2-n·2 1(=22(12分故T=(n-1)·2 1 2.

作文Dear Sir/ madamI'm Li Hua. I' m writing to you to complain about a problem with some books I ordered from yourwebsiteOn 3rd September, greatly delighted, I ordered ten books from your online store, hoping to read all thebooks within three months. It was true that I was greatly excited when the books arrived. However, hardlyhad I seen those books when disappointment quickly struck me because only nine books were lying in theparcel. In addition, what annoyed me more was that only six of them were what I had ordered while theother three were delivered here by mistake. Therefore, could you please arrange for the rest of my orderto be sent to me as soon as possible? Otherwise, please give me a refund. Meanwhile, I would appreciate itif you could let me know what I should do with the three books that I didnt orderI would be extremely grateful if you could look into the matter as soon as possible and get it settled bynext week. I'm looking forward to hearing from you soonLi Hua

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