`a) x = 1/5 + 2/11`
`x= 11/55 + 10/55`
`x = 21/55`
Vậy `x = 21/55`
``
`b) x = 1/13 + (-13)/26`
`x= 1/13 - 1/2`
`x = 2/26 - 13/26`
`x = -11/26`
Vậy `x = -11/26`
``
`c) x = 1/12 + 3/4 + (-2)/9`
`x = 3/36 + 27/36 - 8/36`
`x= 11/18`
Vậy `x = 11/18`
``
`d) x/5 = 5/6 + (-19)/30`
`x/5 = 25/30 - 19/30`
`x/5 = 1/5`
⇒ `x = 1`
Vậy `x = 1`
``
`e) x/7 = 3/7 + (-5)/4``
`x/7 = 12/28 - 35/28`
`x/7 = -23/28`
`x . 28 = 7 . (-23)`
`x . 28 = -161`
`x = -161 : 28`
`x = -23/4`
Vậy `x = -23/4`
``
`f) 11/8 + 13/6 = 85/x`
`33/24 + 52/24 = 85/x`
`85/24 = 85/x`
⇒ `x = 24`
Vậy `x = 24`