Giải:
`c) -5/11 . 4/13 + -5/11 . 9/13 + 3 5/11`
`= -5/11 . 4/13 + -5/11 . 9/13 + 38/11`
`= -5 . (4/13 + 9/13) + 38/11`
`= -5 . 13/13 + 38/11`
`= -5 . 1 + 38/11`
`= (-5) + 38/11`
`= 33/11`
`= 3`
`d) -3/13 - 7/17 + -5/19 + -10/13 + 24/17 - 14/19`
`= (-3/13 + -10/13) - (7/17 - 24/17) + (-5/9 - 14/19)`
`= -13/13 + 17/17 + - 19/19`
`= (-1) + 1 - 1`
`= 0 - 1`
`= - 1`