Đáp án:
$a/$ `M= (-1)/6 - 2/3 . (-3)/4 + (-2)^2/5`
`-> M = (-1)/6 + 1/2 + 4/5`
`-> M = 1/3 + 4/5`
`-> M = 17/15`
`text{Vậy}` `M = 17/15`
$b/$ `2 2/9 - 1 1/9 - 46/5 . 5/23 + 4/3`
`= 20/9 - 10/9 - 2 + 4/3`
`= 10/9 - 2 + 4/3`
`= (-8)/9 + 4/3`
`= 4/9`
$c/$ `N = 2/(3 . 5) + 2/(5 . 7) + 2/(7 . 9) + 2/(9 . 11) + 2/(11 . 13) + 2/(13 . 15)`
`-> N = 1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11 + 1/11 - 1/13 + 1/13 - 1/15`
`-> N = 1/3 + (- 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11 + 1/11 - 1/13 + 1/13) -1/15`
`-> N = 1/3 - 1/15`
`-> N =4/15`
`text{Vậy}` `N = 4/15`