\[\frac{b^{\backslash b - 1}}{b + 1} - \frac{b^{2}}{b^{2} - 1} = \frac{b^{2} - b - b^{2}}{(b - 1)(b + 1)} =\]
\[= - \frac{b}{b^{2} - 1} = \frac{b}{1 - b²}\]