[Toán 11] Dãy số

A

anhtraj_no1

[TEX]U_n=\frac{1-2n}{n}\\ U_{n+1}=\frac{-1-2n}{n+1}\\ \Rightarrow \frac{u_{n+1}}{u_n}=\frac{-2n^2-n}{-2n^2-n+1}=1-\frac{1}{-2n^2-n+1}>1\\ \Rightarrow u_{n+1}>u_n\\ \Rightarrow Day\ tang.[/TEX]
 
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