Tính tổng sau 1/3+1/5.7+1/7.9+...+1/999.1001
2 câu trả lời
`1/3 +1/(5.7)+1/(7.9) + ...+ 1/(999 . 1001)`
`= 1/3 + (1/(5.7)+1/(7.9)+...+1/(999 . 1001))`
`= 1/3 + 1/2 (1/5 - 1/7 +1/7 -1/9 + ... +1/999 - 1/1001)`
`=1/3+1/2(1/5 - 1/1001)`
`= 1/3+1/2 . 996/5005`
`= 1/3+498/5005`
`= 6499/15015`
`1/3 + 1/(5.7) + 1/(7.9) + ... + 1/(999.1001)`
`= 1/3 + (1/(5.7) + 1/(7.9) + ... + 1/(999.1001))`
`= 1/3 + 1/2 . (2/(5.7) + 2/(7.9) + ... + 2/(999.1001) )`
`= 1/3 + 1/2 . (1/5 - 1/7 + 1/7 - 1/9 + ... + 1/999 - 1/1001)`
`= 1/3 + 1/2 . (1/5 - 1/1001)`
`= 1/3 + 1/2 . 996/5005`
`= 1/3 + 498/5005`
`= 6499/15015`
