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Đáp án + Giải thích các bước giải:

 `Bài 1:`

`a)1/6+-5/6=4/6=2/3`

`b)7/-25+-8/25`

`=-7/25+-8/25`

`=-15/25=-3/5`

`c)6/13+-15/39`

`=6/13+-5/13`

`=1/13`

`d)5/7+-4/14`

`=5/7+-2/7`

`=3/7`

`e)-8/18+-15/27`

`=-4/9+-5/9`

`=-9/9=-1`

`Bài 2:`

`a)3/5+-7/4`

`=12/20+-35/20`

`=-23/20`

`b)(-2)+-5/8`

`=-16/8+-5/8`

`=-21/8`

`c)1/-8+-5/9`

`=-9/72+40/72`

`=31/72`

`Bài 3:`

`1)x=-1/2+3/4`

`x=1/4`

Vậy `x=1/4`

`2)X-1/5=2/11`

`x=2/11+1/5`

`x=21/55`

Vậy `x=21/55`

`3)x-5/6=16/42+-8/56`

`x-5/6=5/21`

`x=5/21+5/6`

`x=15/14`

Vậy `x=15/14`

`4)x/5=5/6+-19/30`

`x/5=1/5`

`x=1`

Vậy `x=1`

`5)x=-1/2+3/4`

`x=1/4`

Vậy `x=1/4`

`6)x/15=3/5+-2/3`

`x/15=-1/15`

`x=-1`

Vậy `x=-1`

`8)11/8+13/6=85/x`

`85/24=85/x`

`24=x`

Vậy `x=24`

`7)x-7/8=13/12`

`x=13/12+7/8`

`x=47/24`

Vậy `x=47/24`

`8)x--6/15=4/27`

`x=4/27+-6/15`

`x=-34/135`

Vậy `x=-34/135`

`9)--6/12+x=9/48`

`1/2+x=9/48`

`x=9/48-1/2`

`x=-5/16`

Vậy `x=-5/16`

`10)x-4/6=5/25+-7/15`

`x-4/6=1/5+-7/15`

`x-4/6=3/15+-7/15`

`x-4/6=-4/15`

`x=-4/15+4/6`

`x=2/5`

Vậy `x=2/5`

`11)x-4/5=6/20+-7/3`

`x-4/5=3/10+-7/3`

`x-4/5=-61/30`

`x=-61/30+4/5`

`x=-37/30`

`12)--7/5+x=4/9`

`7/5+x=4/9`

`x=4/9-7/5`

`x=-43/45`

Vậy `x=-43/45`