- #1
synkk
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show that if ## a_n ## is any sequence and m is any integer such that the series ## \displaystyle \sum_{n=m}^\infty a_n ## converges, then ## \displaystyle\lim_{k \to \infty} \sum_{n=k}^{\infty
} a_n = 0 ##
let ## S_N = \displaystyle \sum_{n=m}^N a_n ##
## \lim_{N \to \infty} S_N = l ## from definition
also,
## \lim_{N \to \infty} S_{N-1} = l ##
## S_N - S_{N-1} = a_N ##
## \lim_{N \to \infty} (S_N - S_{N-1}) = \lim_{N \to \infty}(S_N) - \lim_{N \to \infty} S_{N-1} = 0 ## then ## \lim_{N \to \infty} a_N = 0 ## i.e. ## \lim_{N \to \infty} \sum_{n=m}^N a_n = 0 \Rightarrow \lim_{k \to \infty} \sum_{n=k}^{\infty} a_n = 0 ##
as you can see I don't really know how to prove this statement, but I have attempted it.
Could someone show me how I can proceed to do the proof properly?
} a_n = 0 ##
let ## S_N = \displaystyle \sum_{n=m}^N a_n ##
## \lim_{N \to \infty} S_N = l ## from definition
also,
## \lim_{N \to \infty} S_{N-1} = l ##
## S_N - S_{N-1} = a_N ##
## \lim_{N \to \infty} (S_N - S_{N-1}) = \lim_{N \to \infty}(S_N) - \lim_{N \to \infty} S_{N-1} = 0 ## then ## \lim_{N \to \infty} a_N = 0 ## i.e. ## \lim_{N \to \infty} \sum_{n=m}^N a_n = 0 \Rightarrow \lim_{k \to \infty} \sum_{n=k}^{\infty} a_n = 0 ##
as you can see I don't really know how to prove this statement, but I have attempted it.
Could someone show me how I can proceed to do the proof properly?