Tính `5/3.4+5/4.6+5/5.8+5/6.10+….+5/40.78`. 05/08/2021 Bởi Caroline Tính `5/3.4+5/4.6+5/5.8+5/6.10+….+5/40.78`.
Đáp án: `5/(3 . 4) + 5/(4 . 6) + 5/(5 . 8) + 5/(6 . 10) + …. + 5/(40 . 78)` `= 10/(4 . 6) + 10/(6 . 8) + 10/(8 . 10) + 10/(10 . 12) + …. + 10/(78 . 80)` `= 10 . [1/(4. 6) + 1/(6 . 8) + 1/(8 . 10) + 1/(10 . 12) + …. + 1/(78 . 80)]` `= 10 . 1/2 . [1/4 – 1/6 + 1/6 – 1/8 + 1/8 – 1/10 + 1/10 – 1/12 + … + 1/78 – 1/80]` `= 10/2 . [1/4 + (- 1/6 + 1/6 – 1/8 + 1/8 – 1/10 + 1/10 – 1/12 + … + 1/78) – 1/80]` `= 5 . [1/4 – 1/80]` `= 5 . 19/80` `= 19/16` Bình luận
Đáp án: `19/16` Giải thích các bước giải: `5/3.4+5/4.6+5/5.8+5/6.10+….+5/40.78` `=10/4.6+10/6.8+10/8.10+10/10.12+…+10/78.80` `=5.(1/4-1/6+1/6-1/8+1/8-1/10+1/10-1/12+…+1/78-1/80)` `=5.(1/4-1/80)` `=5.19/80` `=19/16` Bình luận
Đáp án:
`5/(3 . 4) + 5/(4 . 6) + 5/(5 . 8) + 5/(6 . 10) + …. + 5/(40 . 78)`
`= 10/(4 . 6) + 10/(6 . 8) + 10/(8 . 10) + 10/(10 . 12) + …. + 10/(78 . 80)`
`= 10 . [1/(4. 6) + 1/(6 . 8) + 1/(8 . 10) + 1/(10 . 12) + …. + 1/(78 . 80)]`
`= 10 . 1/2 . [1/4 – 1/6 + 1/6 – 1/8 + 1/8 – 1/10 + 1/10 – 1/12 + … + 1/78 – 1/80]`
`= 10/2 . [1/4 + (- 1/6 + 1/6 – 1/8 + 1/8 – 1/10 + 1/10 – 1/12 + … + 1/78) – 1/80]`
`= 5 . [1/4 – 1/80]`
`= 5 . 19/80`
`= 19/16`
Đáp án:
`19/16`
Giải thích các bước giải:
`5/3.4+5/4.6+5/5.8+5/6.10+….+5/40.78`
`=10/4.6+10/6.8+10/8.10+10/10.12+…+10/78.80`
`=5.(1/4-1/6+1/6-1/8+1/8-1/10+1/10-1/12+…+1/78-1/80)`
`=5.(1/4-1/80)`
`=5.19/80`
`=19/16`