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