英语周报2018到201答案

I looked at what the second man had dropped; it was jewellery. It all happened too quickly,but I soon realized what had happened. They were burglars. My friend Jeremy, who was waitingfor me, quickly ran out. when hearing unusual noises. We called the police and they were there 5minutes later. I gave the police officer descriptions of the thieves and told them the names theyhad called outYou were brave for trying stop them, "said the officer: We should be able to catch themwith your information. " Jeremy told the officer the owners of the house were on holiday and gavehim a phone number. When the officer left, I told Jeremy about the mistake with the doornumbers. I hadn, t really been brave at all, but my mix-up had stopped the burglars getting awaywith the jewelry. Jeremy's neighbor thanked me a lot when they came back. Actually I have been

(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

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