Giải các phương trình sau : `a, 3x+1=7x-11` `b, 5-3x=6x+7` `c,11-2x=x-1` `d,15-8x=9-5x`

`a)`

`3x+1=7x-11`

`<=>3x-7x=-1-11`

`<=>-4x=-12`

`<=>x=-12:-4`

`<=>x=3`

Vậy `S = {3}`

`b)`

`5-3x=6x+7`

`<=>-3x-6x=-5+7`

`<=>-9x=2`

`<=>x=2:-9`

`<=>x=-2/9`

Vậy S` = {-2/9}`

`c)`

`11-2x=x-1`

`<=>-2x-x=-11-1`

`<=>-3x=-12`

`<=>x=-12:-3`

`<=>x=4`

Vậy `S={4}`

`d)` `15-8x=9-5x`

`<=>-8x+5x=-15+9`

`<=>-3x=-6`

`<=>x=-6:-3`

`<=>x=2`

Vậy `S={2}`