в) $$\frac{x}{x + y} + \frac{y}{x - y}$$;

в) $$\frac{x}{x + y} + \frac{y}{x - y} = \frac{x(x - y) + y(x + y)}{(x + y)(x - y)} = \frac{x^2 - xy + xy + y^2}{(x + y)(x - y)} = \frac{x^2 + y^2}{(x + y)(x - y)} = \frac{x^2 + y^2}{x^2 - y^2}$$.

Ответ: $$\frac{x^2 + y^2}{x^2 - y^2}$$