问题标题:
已知数列an中a1=-2且an+1=sn(n+1为下标),求an,sn
问题描述:

已知数列an中a1=-2且an+1=sn(n+1为下标),求an,sn

李守平回答:
  已知a_(n+1)=S_n得a_n=S_(n-1)(n>1)两式相减a_(n+1)-a_n=S_n-S_(n-1)=a_n(n>1)得a_(n+1)=2a_n(n>1)因为a_2=S_1=a_1=-2所以a_n=-2^(n-1)(n>1,a1=-2);S_n=a_(n+1)=-2^n...
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