數(shù)列與不等式學(xué)案

1、回顧4數(shù)列與不等式 必記知識(shí) 等差數(shù)列設(shè)Sn為等差數(shù)列an的前n項(xiàng)和,則1ana1n1damnmd,若pqmn,則apaqaman.2apq,aqppqapq0;SmnSmSnmnd.3Sk,S2kSk,S3kS2k,構(gòu)成的數(shù)列是等差數(shù)列4。

2、溯源回扣四數(shù)列與不等式1.已知數(shù)列的前n項(xiàng)和Sn求an,易忽視n1的情形,直接用SnSn1表示.事實(shí)上,當(dāng)n1時(shí),a1S1;當(dāng)n2時(shí),anSnSn1.回扣問(wèn)題1在數(shù)列an中,a12n1nN,則an.解析依題意得,數(shù)列的前n項(xiàng)和為2n1,當(dāng)n。

3、溯源回扣四數(shù)列與不等式1.已知數(shù)列的前n項(xiàng)和Sn求an,易忽視n1的情形,直接用SnSn1表示.事實(shí)上,當(dāng)n1時(shí),a1S1;當(dāng)n2時(shí),anSnSn1.回扣問(wèn)題1已知數(shù)列an的前n項(xiàng)和Sn2n3,則an.解析當(dāng)n2時(shí),anSnSn12n2n1。