Question

 Chứng minh  1/1^2+1/3^2+1/5^2+......+1/99^2 <5/4

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Ai nhanh chóng nhất là 3 tick  lun  nha

 

Answer 1

\(\frac{1}{1^2}+\frac{1}{3^2}+\frac{1}{5^2}+....+\frac{1}{99^2}\)

\(< \frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+.....+\frac{1}{98\cdot99}\)

\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+....+\frac{1}{98}-\frac{1}{99}\)

\(=1-\frac{1}{99}\)

\(< 1\)

\(< \frac{5}{4}\)