Упростим

1. a) $$\frac{6 + \sqrt{6}}{\sqrt{30} + \sqrt{5}} = \frac{6 + \sqrt{6}}{\sqrt{5} \cdot \sqrt{6} + \sqrt{5}} = \frac{6 + \sqrt{6}}{\sqrt{5} (\sqrt{6} + 1)} = \frac{\sqrt{6}(\sqrt{6} + 1)}{\sqrt{5} (\sqrt{6} + 1)} = \frac{\sqrt{6}}{\sqrt{5}} = \sqrt{\frac{6}{5}} = \frac{\sqrt{30}}{5}$$
2. б) $$2\sqrt{2} + \sqrt{50} - \sqrt{98} = 2\sqrt{2} + \sqrt{25 \cdot 2} - \sqrt{49 \cdot 2} = 2\sqrt{2} + 5\sqrt{2} - 7\sqrt{2} = 0$$
3. в) $$\frac{4x - y}{2x - \sqrt{xy}} = \frac{(2\sqrt{x} - \sqrt{y})(2\sqrt{x} + \sqrt{y})}{\sqrt{x}(2\sqrt{x} - \sqrt{y})} = \frac{2\sqrt{x} + \sqrt{y}}{\sqrt{x}}$$

Ответ:

1. a) $$\frac{\sqrt{30}}{5}$$
2. б) $$0$$
3. в) $$\frac{2\sqrt{x} + \sqrt{y}}{\sqrt{x}}$$