英语周报 2022-2010九年级 课 1答案

书面表达One possible versionInternational studentsTo enrich our school life and build our body, a hiking with the theme of"Experience the Hutuo River Cul-re"will be held this weekend.As scheduled, any student willing to participate in the activity should gather at the school gate at 8: 00 amon Saturday. We'll walk along the bank of the Hutuo River, going all the way north. At noon, we'll reach abeautiful town, where some experts will tell us history and culture about the river. Finally, we ' ll return by thesame routeMatters needing attention are as follows: uniforms, comfortable shoes, enough water etc.wish you a good journey.

17.(I)设等差数列{an}的公差为d,∵an2=a4+24∴(a1+d)2=(a1+3d)+24,又∵a1=3,∴(3+d)2=(3+3d)+24,解得d=-6或d=3,…………………………………4分∵d>0,∴d=3,∴an=3+3(n-1)=3n,………6分SIna.T(n为奇数)(Ⅱ)∵b。=cesana(n为偶数)∴当n为奇数时,b=sin3nr=sinr=0,∴当n为偶数时,b。=cos3nr=cs0=1,…10分故{b}是以2为周期的周期数列,且b1+b2=1,∴b+b2+…+b201=1010(1+b2)+b1=1010+0=1010.………………12分

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