(frac{{x + 1}}{{x - 1}} - frac{{x - 1}}{{x + 1}}) bằng :

* Hướng dẫn giải

\(\begin{array}{l}
\frac{{x + 1}}{{x - 1}} - \frac{{x - 1}}{{x + 1}} = \frac{{{{\left( {x + 1} \right)}^2} - {{\left( {x - 1} \right)}^2}}}{{\left( {x - 1} \right)\left( {x + 1} \right)}}\\
 = \frac{{{x^2} + 2x + 1 - \left( {{x^2} - 2x + 1} \right)}}{{{x^2} - 1}} = \frac{{4x}}{{{x^2} - 1}}
\end{array}\)