数列{an}的前n项的和Sn=2n-1,则an=_.
问题描述:
数列{an}的前n项的和Sn=2n-1,则an=______.
答
∵数列{an}的前n项的和Sn=2n-1,
∴n=1时,a1=S1=2-1=1;
n≥2时,an=Sn-Sn-1
=(2n-1)-(2n-1-1)
=2n-1.
n=1时,2n-1=1=a1.
∴an=2n−1.
故答案为:2n-1.