Đáp án:`+`Giải thích các bước giải:

 Câu `3:`

` 2/(x-3) + 3/(x+3) <= (4x)/(x^2-9)`

`<=>` `2/(x-3) +3/(x+3)  - (4x)/(x^2-9) <=0`

`<=>` `[2(x+3)]/(x^2-9) + [3(x-3)]/(x^2-9) - (4x)/(x^2-9) <=0`

`<=>` `(2x+6 +3x -9 -4x)/(x^2-9) <=0`

`<=>` `(x-3)/(x^2-9) <=0`

`<=>` `1/(x+3) <=0`

Vì `1>0`

`=>` `x+3 <0`

`<=>` `x<-3`

Câu `4:`

`1) (8x+3)/4 - (3-2x)/3 <= (5-3x)/2 +1`

`<=>` `[3(8x+3)]/12 - [4(3-2x)]/12 <= (5-3x)/2 +2/2`

`<=>` `(24x +9 - 12+8x)/12 <= ( 5-3x+2)/2`

`<=>` `(32x -3)/12 <= (7-3x)/2`

`<=>` `2. (32x-3) <= 12.(7-3x)`

`<=>` `64x - 6 <= 84 -36x`

`<=>` `64x +36x <= 6+84`

`<=>` `100x<=90`

`<=>` `x<=9/10`

Vậy .

 `2) (x+2)/5 - x>= (3x-3)/2 +1/3`

`<=>` `(x+2)/5 - (5x)/5 >= [3(3x-3)]/6 +2/6`

`<=>` `(x+2-5x)/5 >= ( 9x -9 +2)/6`

`<=>` `(2-4x)/5 >= (9x-7)/6`

`<=>` `6.(2-4x) >= 5.(9x-7)`

`<=>` `12 -24x >= 45x -35`

`<=>` `-24x - 45x >= -12 -35`

`<=>` `-69x >=-47`

`<=>` `x<= -47/69`

Vậy .