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mong mọi người giúp đỡ
1/$ \lim \sum \limits_{k=1}^n \dfrac{ 1}{4k^2-1}$
2/$\lim \sum \limits_{k=1}^n \dfrac{ 1}{k(k+3)}$
3/$\lim(1/(5^n).\sum_{k=1}^n 4^k)$
1/$ \lim \sum \limits_{k=1}^n \dfrac{ 1}{4k^2-1}$
2/$\lim \sum \limits_{k=1}^n \dfrac{ 1}{k(k+3)}$
3/$\lim(1/(5^n).\sum_{k=1}^n 4^k)$
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