`3/(1-3x) = 2/(1+3x) - (7-5x)/(9x^2-1)` `( x ne 1/3; -1/3)`

`<=> 3/(1-3x) - 2/(1+3x) - (7-5x)/((1-3x)(1+3x)) =0`

`<=> (3(1+3x))/((1-3x)(1+3x)) - (2(1-3x))/((1-3x)(1+3x))  - (7-5x)/((1-3x)(1+3x)) =0`

`=>3+9x-2+6x -7+5x=0`

`<=>20x-6=0`

`<=> x=6/20`

`<=>x= 3/10(tm)`

Vậy `S={3/10}`

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`1/(x^2-1) + 2/(x-1) = 3/(2x+2)` `(x ne +-1)`

`<=> 1/((x-1)(x+1)) + 2/(x-1) -3/(2(x+1))=0`

`<=> 2/(2(x-1)(x+1)) + (4(x+1))/(2(x-1)(x+1)) - (3(x-1))/(2(x-1)(x+1))=0`

`=>2 + 4x+4 - 3x+3=0`

`<=> x +9=0`

`<=>x=-9(tm)`

Vậy `S={9}`