1) $$\frac{1}{\sqrt[4]{8}} = \frac{1}{\sqrt[4]{2^3}} = \frac{\sqrt[4]{2}}{\sqrt[4]{2^3} \cdot \sqrt[4]{2}} = \frac{\sqrt[4]{2}}{\sqrt[4]{2^4}} = \frac{\sqrt[4]{2}}{2}$$.
2) $$\frac{6}{3\sqrt[4]{4} + \sqrt[3]{2}} = \frac{6}{3\sqrt{2} + \sqrt[3]{2}} = \frac{6(3\sqrt{2} - \sqrt[3]{2})}{(3\sqrt{2} + \sqrt[3]{2})(3\sqrt{2} - \sqrt[3]{2})} = \frac{6(3\sqrt{2} - \sqrt[3]{2})}{18 - \sqrt[3]{4}}$$.
Ответ: 1) $$\frac{\sqrt[4]{2}}{2}$$; 2) $$\frac{6(3\sqrt{2} - \sqrt[3]{2})}{18 - \sqrt[3]{4}}$$.