A
aspiration


chứng minh:
[TEX]{1 \over 5}+{1 \over 13}+{1 \over 25}+...+{1 \over {2008^{2}+2009^{2}}}<{1 \over 2}[/TEX]
[TEX]{1 \over 5}+{1 \over 13}+{1 \over 25}+...+{1 \over {2008^{2}+2009^{2}}}<{1 \over 2}[/TEX]
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