I have a question which is giving me a hard time.
I want to show that limn→∞1nn∑k=1xk=x given that limn→∞xn=x.
Answer
Or you could slog through a tedious proof:
Choose ϵ>0. Let N be such that n≥N means |xn−x|<ϵ2. Now choose N′≥N so that n≥N′ means 1n∑Nk=1|xn−x|<ϵ2.
Then, if n≥N′, we have the estimate:
|1nn∑k=1(xn−x)|≤1nn∑k=1|xn−x|≤1nN∑k=1|xn−x|+1nn∑k=N+1|xn−x|<ϵ2+n1nϵ2=ϵ
Hence limn→∞1n∑nk=1(xn−x)=0 from which the result follows.
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