Tham khảo
` \frac{3^2}{24.27}+\frac{3^2}{27.29}+...+\frac{3^2}{72.75}`
`=3.( \frac{3}{24.27}+\frac{3}{27.29}+...+\frac{3}{72.75})`
Áp dụng công thức `\frac{3}{n(n+3)}=\frac{1}{n}-\frac{1}{n+3}`
`=3.(\frac{1}{24}-\frac{1}{27}+\frac{1}{27}-\frac{1}{29}+....+\frac{1}{72}-\frac{1}{75})`
`=3.(\frac{1}{24}-\frac{1}{75})`
`=3.\frac{17}{600}`
`=\frac{17}{200}`
`\text{©CBT}`