Đáp án:
`4/7 . (8/-13) + 4/7 .((-2)/3) + 1 3/13 . ((-4)/7)`
`= 4/7 . (-8/13) + 4/7 . (-2/3) + 16/13 . ((-4)/7)`
`= 4/7 . (-8/13) + 4/7 . (-2/3) + (-16/13) . 4/7`
`= 4/7 (-8/13 - 2/3 - 16/13)`
`= 4/7 (-24/39 - 26/39 - 48/39)`
`= 4/7 . (-98/39)`
`= - 56/39`
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