英语周报 2018-2022.答案

17【解析】(I)由题意,a1=9=6,又数列{a}是公差为2的等差数列,a=6+2(n-1)=2n+4,含++…430当心2时,十备十含大合,①一②得aa,1=2,即∴b=2(n+1)(m≥2)∴b=(12,n=12n+2,n≥2.……6分)当”≥3时,:-+4·m+2-(n+1)(n+2)-44+所以S,=1.1+11+…+1+号一÷→(n+2)4(18-n+2)-72(n+2)·1一2也足上式∴S,472(n+2)·……………………………12分

书面表达One possible version:Dear Mr. Smith.First of all, I would like to congratulate you on your school s sixtieth anniversary. The long history of theschool brings up its outstanding campus culture and educational concept. I take great pride in studying at thisexcellent school, At your invitation, I will perform a Chinese folk dance at the celebration ceremony to expressmy congratulations. Please prepare the audio equipment to play the accompanying music. I will prepare thedance music and costumes myself. I am delighted to be able to make a modest contribution to the promotion ofChinese culture and cultural exchanges between China and the UKBest wishes.Yours truly,Li Hu

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