L
leducsang1997


1.Tính
A=[TEX](1-\frac{1}{2^2})(1-\frac{1}{3^2}).....(1-\frac{1}{1999^2})[/TEX]
2.CMR
a/[TEX]\begin{matrix}\underbrace{99\cdots9^2}\\n\end{matrix}=\begin{matrix}\underbrace{99\cdots9}\\n-1\end{matrix}\begin{matrix}\underbrace{800\cdots01}\\n+1\end{matrix}[/TEX]
A=[TEX](1-\frac{1}{2^2})(1-\frac{1}{3^2}).....(1-\frac{1}{1999^2})[/TEX]
2.CMR
a/[TEX]\begin{matrix}\underbrace{99\cdots9^2}\\n\end{matrix}=\begin{matrix}\underbrace{99\cdots9}\\n-1\end{matrix}\begin{matrix}\underbrace{800\cdots01}\\n+1\end{matrix}[/TEX]
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