30. a) x2-y2/(x + y) 2;

30. а) $$\frac{x^2-y^2}{(x+y)^2} = \frac{(x-y)(x+y)}{(x+y)^2} = \frac{x-y}{x+y}$$

Ответ: $$\frac{x-y}{x+y}$$