`a)(x/(x-1)+x/(x^2-1)):(2/x^2-(2-x^2)/(x^3+x^2))`
`đkxđ :` `x#±1;x#0`
`=([x(x+1)]/(x^2-1)+x/(x^2-1)):([2(x+1)]/[x^2(x+1)]-(2-x^2)/[x^2(x+1)))`
`=[x^2+x+x]/[x^2-1):[2x+2-2+x^2]/[(x^2)(x+1)]`
`=[x^2+2x]/(x^2-1):[x^2+2x]/(x^2(x+1)`
`=[x^2+2x]/(x^2-1).(x^2(x+1))/[x^2+2x]`
`=x^2/(x-1)`
`b)A=4`
`<=>x^2/(x-1)=4`
`=>4(x-1)=x^2`
`<=> 4x-4=x^2`
`<=>-x^2+4x-4=0`
`<=>-(x-2)^2=0`
`<=>`\(\left[ \begin{array}{l}-x+2=0\\x-2=0\end{array} \right.\) `=>` \(\left[ \begin{array}{l}x=2(tm)\\x=2(tm)\end{array} \right.\)
vậy `x=2`
`c)A<0`
`=>x^2/(x-1)<0`
`=>x-1<0(`vì `x^2≥0)`
`=>x<1`
vậy `x<1`
