Đáp án:+Giải thích các bước giải:
`a, A = 1/3 . 4/5 + 1/3 . 6/5 + 2/3`
`A = 1/3 . (4/5 + 6/5) + 2/3`
`A = 1/3 . 2 + 2/3`
`A = 2/3 + 2/3`
`A = 4/3`
`b, B = 7/8 + 1/8 . 3/8 + 1/8 . 5/8`
`B = 7/8 + 1/8 . (3/8 + 5/8)`
`B = 7/8 + 1/8 . 1`
`B = 1`
`c, C = -5/6 . 4/19 + -7/12 . 4/19 - 40/57`
`C = 4/19 . ( -5/6 - 7/12) - 40/57`
`C = 4/19 . -17/12 - 40/57`
`C = -17/57 - 40/57`
`C = -1`
`d, D = 3/7 . 9/26 - 1/14 . 1/13 - 1/7`
`D = 1/13 . ( 3/7 . 9/2 - 1/14 ) - 1/7`
`D = 1/13 . ( 27/14 - 1/14 ) - 1/7`
`D = 1/13 . 13/7 - 1/7`
`D = 1/7 - 1/7`
`D = 0`