Đáp án:
$\begin{array}{l}
\frac{2}{{3x}} - \frac{2}{{x + 1}}.\left( {\frac{{x + 1}}{{3x}} - x - 1} \right):\frac{{x - 1}}{x}\\
= \frac{2}{{3x}} - \frac{2}{{x + 1}}.\left( {x + 1} \right).\left( {\frac{1}{{3x}} - 1} \right).\frac{x}{{x - 1}}\\
= \frac{2}{{3x}} - 2.\frac{{1 - 3x}}{{3x}}.\frac{x}{{x - 1}}\\
= \frac{2}{{3x}} - \frac{2}{{3x}}.\frac{{x\left( {1 - 3x} \right)}}{{x - 1}}\\
= \frac{2}{{3x}}.\left( {1 - \frac{{x\left( {1 - 3x} \right)}}{{x - 1}}} \right)\\
= \frac{2}{{3x}}.\frac{{x - 1 - x + 3{x^2}}}{{x - 1}}\\
= \frac{2}{{3x}}.\frac{{3{x^2} - 1}}{{x - 1}}\\
= \frac{{6{x^2} - 2}}{{3{x^2} - 3x}}
\end{array}$
