2021-2022 英语周报 八年级 新课程 47答案

第二节书面表达Dear Sir/MadamJust now I came to turn in our English homework fortoday. However, I failed to report it to you face to faceThat's why I leave you the notWe have 56 students in our class in total, so weshould have handed in 56 copies of our exercise books. Butunfortunately one of my classmates got ill this morning andasked for a leave and is still staying at home. Besidesanother two students are art students, who were busywith their major practice yesterday, As a result,theyhaven't finished the homework yet. Anyhow they havepromised that they will finish it tonight and turn it intomorrow morningTo sum up, all the 56 students except the threementioned above, 53 altogether, have turned in theirhomeworkHave a nice dayLi Hua听力录音

20.解:(1)由2s+ra=r+5即2Sn+2a=n2+5n+2,①1分所以a1=2,由①得2S1+2a-1=(n-1)2+5(n-1)+2(n≥2),②①-②,得2an=am-1+n+2(n≥2)2分当n=2时,2a2=a1+1+2,a2=3;3分当n=3时,2a=a+3+2,a3=4;当n=4时,2a=a3+4+2,a4=5分(2)由(1)猜想an=n+1.下面用数学归纳法证明:①当n=1时,由(1)可知猜想成立;8分②假设n一k时猜想成立即a=+1此时2S+20=+5+2,S=(++2)-4=号+号9分贮2+3当n=k+1时,S+1=S+a+1=2(k+1)2+3(k10分整理得a+1=(k+1)+111分所以当n=k+1时猜想成立综上所述:对任意n∈N,an=n+1成立12分

以上就是2021-2022 英语周报 八年级 新课程 47答案，更多英语周报答案请关注本网站。