(优辅资源)版四川省成都市高一下学期期末考试数学试题 Word版含答案

全优好卷

22、解:(Ⅰ)?1211?(?1)n??(?1)n?(?2)[?(?1)n?1], ,?anan?1anan?1 又?4分

?11n??(?1)?3,?数列????1??是首项为3,公比为?2的等比数列.……a1?an?(?1)n?11(2n?1)?n?1?(Ⅱ)?sin. ?(?1),?bn?3(?2)n?1?(?1)n3?2n?1?12 ?cn??2?1n???1??n?2n 3?bn?+

∴Sn=1×2+2×22+3×23+…+n×2n,①

2Sn=1×22+2×23+3×24+…+(n-1)×2n+n×2n1.② ①-②,得—Sn=2+2+2+…+2-n·2

23nn+1

2?1-2n?+++

=-n·2n1=2n1-n·2n1-2.

1-2

∴Sn=(n-1)2n1+2.…………………………………………8分 (Ⅲ) 当n?3时,则Tn?1111 ?????3?13?2?13?22?13?2n?1?1112n?2[1?(1)]2 11?21111111???????473?223?233?2n?128?111111147484?[1?()n?2]?????. 2862286848474 ?T1?T2?T3, ?对任意的n?N?,Tn?. …………………………12分

7

全优好卷

联系客服:779662525#qq.com(#替换为@)