Đáp án:

Giải thích các bước giải:

`a) 5+2x = 20-3x`

`⇔ 5+2x-20+3x=0`

`⇔ 5x-15=0`

`⇔5x=15`

`⇔x=3`

Vậy `S={3}`

`b) 7-(2x+4)=-(x+4)`

`⇔ 7-2x-4 = -x-4`

`⇔3-2x+x+4=0`

`⇔ -x+7=0`

`⇔-x=-7`

`⇔x=7`

Vậy `S={7}`

`c) (5x+2)-3(2x+1)=-3x+7`

`⇔5x+2-6x-3+3x-7=0`

`⇔ 2x-8=0`

`⇔ 2x=8`

`⇔x=4`

Vậy `S={4}`

`d) 2x-(3-5x) = 4(x+3)`

`⇔ 2x-3+5x=4x+12`

`⇔ 7x-3-4x-12=0`

`⇔ 3x-15=0`

`⇔3x=15`

`⇔x=5`

Vậy `S={5}`

`e) 5(2x-3)-4(5x-7)=19-2(x+11)`

`⇔ 10x-15 - 20x + 28 = 19 - 2x - 22`

`⇔ -10x + 13 = -3 - 2x`

`⇔ -10x + 13 + 3 + 2x=0`

`⇔ -8x+16=0`

`⇔-8x=-16`

`⇔x=2`

Vậy `S={2}`

`f) 5x+7=2(x-1)`

`⇔5x+7=2x-2`

`⇔5x+7-2x+2=0`

`⇔3x+9=0`

`⇔3x=-9`

`⇔x=-3`

Vậy `S={-3}`