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