`9) 3/11 × 7/19 + 17/11 × 3/19 - 3/19 × 13/11`
`= 3/19 × 7/11 + 17/11 × 3/19 - 3/19 × 13/11`
`= 3/19 × (7/11 + 17/11 - 13/11)`
`= 3/19 × 1`
`= 3/19`
`10) 6/7 × 8/13 + 6/13 × 9/7 - 4/13 × 6/7`
`= 6/7 × 8/13 + 6/7 × 9/13 - 4/13 × 6/7`
`= 6/7 × (8/13 + 9/13 - 4/13)`
`= 6/7 × 1`
`= 6/7`
`11) 5/9 × 7/13 + 5/9 × 9/13 - 5/9 × 3/13`
`= 5/9 × (7/13 + 9/13 - 3/13)`
`= 5/9 × 1`
`= 5/9`
`12) 5/12 × 6/11 + 5/12 × 5/11 + 7/12`
`= 5/12 × (6/11 + 7/11) + 7/12`
`= 5/12 × 1 + 7/12`
`= 5/12 + 7/12`
`= 12/12 = 1`
`13) 7/19 × 8/11 + 7/19 × 3/11 + 12/19`
`= 7/19 × (8/11 + 3/11) + 12/19`
`= 7/19 × 1 + 12/19`
`= 7/19 + 12/19`
`= 19/19 = 1`
`14) 5/11 × 18/29 - 5/11 × 8/29 + 5/11 19/29`
`= 5/11 × (18/29 - 8/29 + 19/29)`
`= 5/11 × 1`
`= 5/11`
`text(Bạn bảo "Các bn chỉ cần lm câu 9,11,10,12,13,14thui ạ" nên mình làm vậy)`