Giải thích các bước giải:
`a)`
`-13/7 . 16/35 . 7/(-13)`
`=(-13.16.7)/(7.35.(-13))`
`=(-13.16.7)/(7.7.5.(-13))`
`=16/(7.5)`
`=16/35`
`b)`
`3/4 . 7/4+3/4 . 18/25`
`=3/4. (7/4+18/25)`
`=3/4 . 247/100`
`=741/400`
`c)`
`7/5 . 8/19 + 7/5 . 12/19 -7/5 . 1/9`
`=7/5 . (8/19+12/19-1/9)`
`=7/5 . (20/19-1/9)`
`=7/5 . (180/171-19/171)`
`=7/5 . 161/171`
`=1127/855`