Question

[Trần Ngọc Ánh]

1.Tìm số hữu tỉ x:

a)\(\frac{x+1}{10}+\frac{x+1}{11}+\frac{x+1}{12}=\frac{x+1}{13}+\frac{x+1}{14}\)

b)\(\frac{x+4}{2000}+\frac{x+3}{2001}=\frac{x+2}{2002}+\frac{x+1}{2003}\)

2.CMR:

a)\(\frac{1}{1.2}+\frac{1}{3.4}+\frac{1}{5.6}+...+\frac{1}{49.50}=\frac{1}{26}+\frac{1}{27}+\frac{1}{28}+...+\frac{1}{50}\)

b)Cho  \(A=\frac{1}{1.2}+\frac{1}{3.4}+\frac{1}{5.6}+...+\frac{1}{99.100}\)

   Chứng minh rằng : \(\frac{7}{12}< A< \frac{5}{6}\)      

Answer 1

[Nguyễn Thị Anh]

Answer 2

[Trần Ngọc Ánh]

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