`2/[x+1]+1/[2x]=[3x-1]/[(x+1)(x-2)]` `ĐK: x \ne 0,x \ne -1,x \ne 2`
`<=>[4x(x-2)+(x+1)(x-2)]/[2x(x+1)(x-2)]=[2x(3x-1)]/[2x(x+1)(x-2)]`
`=>4x^2-8x+x^2-2x+x-2=6x^2-2x`
`<=>x^2+7x+2=0`
`<=>x^2+2.x. 7/2+49/4-41/4=0`
`<=>(x+7/2)^2=41/4`
`<=>|x+7/2|=\sqrt{41}/2`
`<=>x=[-7+-\sqrt{41}]/2` (t/m)
Vậy `S={[-7+-\sqrt{41}]/2}