giúp em với

N

nhithithu

Ta có:[TEX]\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...[TEX][/TEX][/TEX]+[TEX]\frac{1}{10^2}[/TEX]
<[TEX]\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+[/TEX][TEX]\frac{1}{9.10}[/TEX]
<[TEX]1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9.10}[/TEX]
<[TEX]1-\frac{1}{10}[/TEX]
<[TEX]\frac{9}{10}<1[/TEX]
\RightarrowD<1
 
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