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heroineladung


Bài tập: Tìm x:
[TEX]\frac{1}{3} + \frac{1}{6} + \frac{1}{10} + ...+ \frac{2}{x(x+1)} = \frac{2007}{2009}[/TEX]






























[TEX]\frac{1}{3} + \frac{1}{6} + \frac{1}{10} + ...+ \frac{2}{x(x+1)} = \frac{2007}{2009}[/TEX]