\[\boxed{\text{167\ (167).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ \frac{a + b}{a - b}\ \ при\ a = \frac{1}{1 - x};\ \ \ \ \]
\[b = \frac{1}{1 + x}\]
\[\textbf{б)}\ \frac{\text{ax}}{a + x} - \frac{\text{bx}}{b - x}\ при\ x = \frac{\text{ab}}{a - b}\]
\[\frac{a \cdot \frac{\text{ab}}{a - b}}{a^{\backslash a - b\ } + \frac{\text{ab}}{a - b}} - \frac{b \cdot \frac{\text{ab}}{a - b}}{b^{\backslash a - b} - \frac{\text{ab}}{a - b}} =\]