Đáp án:
`B = \frac{1}{3.5} + \frac{1}{5.7} + ... + \frac{1}{97.99}`
`2 . B = 2 . (\frac{1}{3.5} + \frac{1}{5.7} + ... + \frac{1}{97.99})`
`2 . B = \frac{2}{3.5} + \frac{2}{5.7} + ... + \frac{2}{97.99}`
`2 . B = \frac{1}{3} - \frac{1}{5} + \frac{1}{5} - \frac{1}{7} + ... + \frac{1}{97} - \frac{1}{99}`
`2 . B = \frac{1}{3} - \frac{1}{99}`
`2 . B = \frac{32}{99}`
`B = \frac{32}{99} : 2`
`B = \frac{16}{99}`
Chúc học tốt!!!
