Đáp án:
Giải thích các bước giải:
Bài `1:`
`a) 3/5 - (-2/3)`
`= 3/5 + 2/3 = 9/15 + 10/15 = ( 9 + 10 ) / 15 = 19/15`
`b) 4/9 . 7/13 + 4/9 . 8/13 + 4/13 . 2/9`
`= 4/9 . (7/13 + 8/13) + 8/117`
`= 4/9 . 15/13 + 4/9 . 2/13`
`= 4/9 . ( 15/13 + 2/13 )`
`= 4/9 . 17/13 = 68/117`
`c) (1/5 - 1/3 + 2/15) -: 2014/2015`
`= [ ( 1/5 + 2/15 ) - 1/3 ] -: 2014/2015`
`= ( 1/3 - 1/3 ) -: 2014/2015`
`= 0 -: 2014/2015 = 0`
Bài `2:`
`a) x + 5/12 = -2/3`
`=> x = -2/3 - 5/12 `
`=> x = -13/12`
Vậy `x=-13/12`
`b) 2/9 - 7/8x = 1/3`
`=> 7/8x = 2/9 - 1/3`
`=> 7/8x = -1/9`
`=> x = -1/9 -: 7/8 `
`=> x = -8/63`
Vậy `x=-8/63`
`c) x + 2/5x = -3/25`
`=> 7/5x = -3/25`
`=> x = -3/25 -: 7/5`
`=> x = -3/35`
Vậy `x=-3/35`
Bài `3:`
`-12/16 = 15/x = y/(-24) = -z/8`
`=> -3/4 = 15/x = y/(-24) = -z/8`
`+) -3/4 = 15/x => -3x=60 => x=-20`
`+) -3/4=y/(-24) => 4y=72 => y=18`
`+) -3/4=-z/8 => 4z=24 => z=6`
Vậy `(x;y;z)=(-20;18;6)`
