2022英语周报 八年级 新目标 12期答案

(17)(本小题满分12分)解:(1)当n=1时,a1=3S-2=3a1-2,解得a1=1当n≥2时,an=3。-2,an1=3Sn1-2,两式相减得anan1=3a化简得an=an→,所以数列{a2}是首项为1,公比为一的等比数列所以(Ⅱ)由(可得m方法一:错位相减法(22(2)*((2)中(2(w(两式相减得2=1+(2所以数列的和({3()……12分方法二:裂项相消法因为=:(2-c-(33)((3)(所以=(-c2)+(2c)+…+(cn-cn)=×、12分

第三节书面表达wersionDear Sir or MadamMy name is Li Hua. As an exchange student fromChina, I am studying in a local school. I am reallydelighted to learn that a volunteer for your Chinese culturallic exhibition is required and I'm confident that I amtruly fit for thestart with, my advantage first lies in the fact that IChina and used to beand quite familiar with Chinese relics. Further-more, being an outgoing and optimistic boy, I am good atcommunicating with others and introducing Chinese cultureto the world is always my honor and my pleasure. Finallythere is no problem with my spoken English, as I havelived here for almost a year and I have no difficulty commu-dicating with others in EnglishI would really appreciate it if you can offer me thechance to be a volunteer in your museum. I am looking forward to your early reply.Li Hua

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