а) \(\frac{1}{3}\sqrt{18} + 3\sqrt{8} - \sqrt{98} = \frac{1}{3}\sqrt{9 \cdot 2} + 3\sqrt{4 \cdot 2} - \sqrt{49 \cdot 2} = \frac{1}{3} \cdot 3\sqrt{2} + 3 \cdot 2\sqrt{2} - 7\sqrt{2} = \sqrt{2} + 6\sqrt{2} - 7\sqrt{2} = (1 + 6 - 7)\sqrt{2} = 0\sqrt{2} = 0\)
Ответ: 0.