1/22+1/32+...+1/20092<1/1.2+1/2.3+...+1/2008.2009
...... <1/1-1/2+1/2-1/3+...+1/2008-1/2009
...... <1/1-1/2009<1
vậy 1/22+11/32+....+1/20092<1
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