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Sir admitere

Posted: Mon May 25, 2009 4:47 pm
by c.adryan
Fie sirul \( a_n=\sum_{k=1}^n{\frac{k(k+1)}{2x^{k-1}}} \) si \( |x|>1 \) Calculati \( \lim_{n \to \infty} a_n \)