新目标遵义英语周报九年级2022––2022答案

18,(本小题满分12分)解:(1)若选择条件①a1=2,则放在第一行的任何一列,满足条件的等差数列{an}都不存在若选择条件②a1=1,则放在第一行第二列,结合条件可知a1=1,a2=4,a3=7,则an=3n-2,n∈N若选择条件③a1=3则放在第一行的任何一列,满足条件的等差数列{an}都不存在综上可知:an=3n-2(2)由(1)知,b=(-1)(3n-2)2所以当n为偶数时Tn=b+b2+b3+…+bn=a2-a2+a32-an2+…+an12-an2(a1+a2Xa1-a2)+(a-a)a3+a1)+…+(an1+a1)an1-a,=-3a1+a2+a3+…a)=-3xm01+3n-2)92,3一n当n为奇数时,=7,+=-90m1+0=1+39n2mn2+2n,m为偶数3n2-=n-2n奇数

书面表达One posssible versionDear Mr. Smith,I'm Li Hua, a senior 3 student. Learning that your City Culture department is looking for an English editorthis summer, I'm eager to apply for the position.As far as I'm concerned, city culture refers to a citys history, geography, customs, future, and so on. Asa native, I am quite familiar with our citys traditional culture. Besides, I have a good command of ErI' m especially good at English writing. Additionally, Im cooperative and creative, which will give me anadvantage for the position.I'll be greatly honored if I' m chosen for the job. If I'm admitted, please email me at lihua @16com.Yours sincerely,Li Hu

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