\(\frac{{x + 1}}{{x - 1}} - \frac{{x - 1}}{{x + 1}...

D

- Hướng dẫn giải

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