已知数列[An]的前n项和为Sn,若Sn=3n-2则a3=
问题描述:
已知数列[An]的前n项和为Sn,若Sn=3n-2则a3=
答
a3 = Sn - Sn-1 = 3n-2 - [3(n-1) -2] = 3
已知数列[An]的前n项和为Sn,若Sn=3n-2则a3=
a3 = Sn - Sn-1 = 3n-2 - [3(n-1) -2] = 3