2015-II-31

15-06-2023 app.cch 尚無留言

答案：C

\begin{array}{cl} \frac{1}{x^{2} - 2 x + 1} - \frac{1}{x^{2} + x - 2} \\ = & \frac{1}{(x - 1)^{2}} - \frac{1}{(x - 1) (x + 2)} \\ = & \frac{(x + 2) - (x - 1)}{(x - 1)^{2} (x + 2)} \\ = & \frac{3}{(x - 1)^{2} (x + 2)} \end{array}