Решение:

1. a) $$\frac{a-y}{\sqrt{a}+\sqrt{y}} = \frac{(\sqrt{a} - \sqrt{y})(\sqrt{a} + \sqrt{y})}{\sqrt{a} + \sqrt{y}} = \sqrt{a} - \sqrt{y}$$
2. б) $$\frac{x+\sqrt{5}}{x^2-5} = \frac{x+\sqrt{5}}{(x-\sqrt{5})(x+\sqrt{5})} = \frac{1}{x-\sqrt{5}}$$