$$\frac{1}{x-y} - \frac{1}{(x-y)^2} = \frac{x-y}{(x-y)^2} - \frac{1}{(x-y)^2} = \frac{x-y-1}{(x-y)^2}$$
Ответ: $$\frac{x-y-1}{(x-y)^2}$$