Giải thích các bước giải:
\(\begin{array}{l}
a)\,\,DKXD:\,x \ne 1\\
b)\,\\
H = \left( {\frac{1}{{x - 1}} - \frac{{2x}}{{{x^3} + x - {x^2} - 1}}} \right):\left( {1 - \frac{{2x}}{{{x^2} + 1}}} \right)\\
H = \left( {\frac{1}{{x - 1}} - \frac{{2x}}{{\left( {x - 1} \right)\left( {{x^2} + 1} \right)}}} \right):\left( {\frac{{{x^2} + 1 - 2x}}{{{x^2} + 1}}} \right)\\
H = \frac{{{x^2} + 1 - 2x}}{{\left( {x - 1} \right)\left( {{x^2} + 1} \right)}} \cdot \frac{{{x^2} + 1}}{{{x^2} + 1 - 2x}}\\
H = \frac{1}{{x - 1}}.\\
c)\,H > 0 \Leftrightarrow \frac{1}{{x - 1}} > 0 \Leftrightarrow x - 1 > 0 \Leftrightarrow x > 1.
\end{array}\)
