2022英语周报课标西北第9期答案

4d=917.()设{a的公差为则由题意得5a1+d=25解得:a1=1,d=24分数列{an}的通项公式为an=a1+(n-1)d=1+2(n-1)=2n-1,即an=2n-1.(2)0)()的项和为S,=(+)2(+20-)7.…………8分的前n项和为:222=1-(2………11分故T12分

写作Dear OliverKnowing that you are returning to your homeland, I am reluctant to saygoodbye to you.【高分句型一】(表达对Over的不舍之情)As for the gift, after careful consideration I recommend you the Chineseknot. Made of red threads, it always represents happiness, luck andunity, though in different shapes. It is a tradition for Chinese to hang it inhouses as a decoration,【高分句型二】 It is usually given as a precious gift toclose friends. I think it can convey your best wishes to your friend.(BF-种礼物并说明原因)Hope my advice can be of some help.(希里)Yours, Li Hua

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