Đáp án:
`c)`
`3/7 . 5/13 - 8/13 . 3/7 + 3/7 . 16/13`
`= 3/7 . ( 5/13 - 8/13 + 16/13 )`
`= 3/7 . 13/13 = 3/7 . 1 = 3/7`
`d)`
`1,25 . 7/19 + 5/4 . 15/19 - 1 1/4 . 3/19`
`= 5/4 . 7/19 + 5/4 . 15/19 - 5/4 . 3/19`
`= 5/4 . ( 7/19 + 15/19 - 3/19 )`
`= 5/4 . 19/19 = 5/4 . 1 = 5/4`
`e)`
`(-5)/17 . (-9)/23 + 9/23 . (-22)/17 + 11 9/23`
`= 5/17 . 9/23 + 9/23 . (-22)/17 + 11 + 9/23`
`= 9/23 . ( 5/17 + (-22)/17 + 1 ) + 11`
`= 9/23 . 0 + 11 = 0 + 11 = 11`
`g)`
`(-11)/19 . 4/13 + (-11)/13 . 15/19 + 11/13`
`= 11/13 . 4/19 + (-11)/13 . 15/19 + 11/13`
`= 11/13 . ( 4/19 + (-15)/19 + 1 )`
`= 11/13 . 0 = 0`