Đáp án:
`a, 13/240` và `-7/80`
`13/240`
`-7/80 = (-7 xx 3)/(80 xx 3) = -21/240`
`b,5/21 ; 3/28 ; 45/108`
`5/21 = (5 xx 36)/(21 xx 36) = 180/756`
`3/28 = (3 xx 27)/(28 xx 27) = 81/756`
`45/108 = (45 xx 7)/(108 xx 7) = 315/756`
`c, 4/35 ; 1/28 ; 39 / 269`
`4/35 = (4 xx 1076)/(35 xx 1076) =4304/37660 `
`1/28 = (1 xx 1345)/(28 xx 1345) = 1345/37660`
`39/269 = ( 39 xx 140)/(269 xx 140) = 5460/37660`