英语周报2018-2022高二第四期答案

第一节图,男ble version:Dear allenHow are you doing? I'm writing to invite you to a lecture on Chinese calligraphy, which will be held by ourschool's calligraphy club next Monday afternoon in the school library. In China calligraphy is not only a means ofcommunication, but also a means of expressing a persons inner world.The lecture will last from 2 pm to 5 pm. The lecturer, who is from Peking University, will mainly talkabout the development of Chinese calligraphyYours sincerely.

17解:(1)因为数列{an}为等差数列,所以设其首项为a1,公差为d,则由a2+a1=30,得2a1+12d=30→a1+6d=15,①又由S20=440得S=20a1+20×192×d=440→2a1+19d=44,②所以由①②得a1=3,d=2所以an=2n+1(4分所以由bn=2-1得bn=22=4(6分)(2)由(1)可知2n+1(7分)所以T=+2+42+…+=ax+双++…+2n+1(8分)所,=是+++…+n-12m+1十1(9分)上述两式相减得Tn=+42++,a++…+22n+14”4+2,22+2+…+22n+14n+1+1×24"2n+114n+1422n+13×44n+1(11分)所以T=12-60+11199×4n9(12分)

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