a) lx-2l+3x = 7 b) l2x+3l = x-4 c) l1-xl - 3x=2 d) l3x+4l -x-1=0

`a)` `|x-2|+3x=7` ĐK`:≤7/3`

`⇔ |x-2|=7-3x` 

`Th` `1:`

`x-2=7-3x`

`⇔ x+3x=7+2`

`⇔ 4x=9`

`⇔ x=9/4` `(tm)`

`Th` `2:`

`x-2=-7+3x`

`⇔ x-3x=-7+2`

`⇔ -2x=-5`

`⇔ x=5/2` `(ktm)`

Vậy `S={9/4}`

`b)` `|2x+3|=x-4` ĐK`:x>=4`

`Th` `1:`

`2x+3=x-4`

`⇔ 2x-x=-4-3`

`⇔ x=-7` `(ktm)`

`Th` `2:`

`2x+3=-x+4`

`⇔ 2x+x=4-3`

`⇔ 3x=1`

`⇔ x=1/3` `(ktm)`

Vậy phương trình vô nghiệm

`c)` `|1-x|-3x=2` ĐK`:x≥-2/3`

`⇔ |1-x|=2+3x `

`Th` `1:`

`1-x=2+3x`

`⇔ -x-3x=2-1`

`⇔ -4x=1`

`⇔ x=-1/4` `(tm)`

`Th` `2:`

`1-x=-2-3x`

`⇔ -x+3x=-2-1`

`⇔ 2x=-3`

`⇔ x=-3/2` `(ktm)

Vậy `S={-1/4}`

`d)` `|3x+4|-x-1=0` ĐK`:x≥-1`

`⇔ |3x+4|=x+1` 

`Th` `1:`

`3x+4=x+1`

`⇔ 3x-x=1-4`

`⇔ 2x=-3`

`⇔ x=-3/2` `(ktm)`

`Th` `2:`

`3x+4=-x-1`

`⇔ 3x+x=-1-4`

`⇔ 4x=-5`

`⇔ x=-5/4` `(ktm)`

Vậy phương trình vô nghiệm