`a)1/(3-x)-1/(x+1)=x/(x-3)-(x-1)^2/(x^2-2x-3)` `(ĐK:x<>3;x<> -1)`
`<=>-1/(x-3)-1/(x+1)=x/(x-3)-(x-1)^2/((x+1)(x-3))`
`<=>(-(x+1))/((x+1)(x-3))-(x-3)/((x+1)(x-3))=(x(x+1))/((x+1)(x-3))-(x-1)^2/((x+1)(x-3))`
`<=>-(x+1)-(x-3)=x(x+1)-(x-1)^2`
`<=>-x-1-x+3=x^2+x-(x^2-2x+1)`
`<=>-2x+2=x^2+x-x^2+2x-1`
`<=>-2x+2=3x-1`
`<=>2x+3x=1+2`
`<=>5x=3`
`<=>x=3/5` (tm)