1. 计算：
(1) $ 3\sqrt{2} + 2\sqrt{2} $； (2) $ 3\sqrt{3} - \sqrt{12} $； (3) $ 3\sqrt{18} + \sqrt{32} - \sqrt{50} $；
(4) $ \sqrt{27} - \sqrt{12} + \sqrt{\dfrac{1}{3}} $； (5) $ 3\sqrt{40} - \sqrt{\dfrac{2}{5}} - 2\sqrt{\dfrac{1}{10}} $； (6) $ \sqrt{0.5} - \sqrt{3.2} - 2\sqrt{0.125} + \sqrt{20} $。
答案：1. (1) $ 5\sqrt{2} $ (2) $ \sqrt{3} $ (3) $ 8\sqrt{2} $ (4) $ \frac{4\sqrt{3}}{3} $ (5) $ \frac{28}{5}\sqrt{10} $ (6) $ \frac{6}{5}\sqrt{5} $
解析：
(1) $3\sqrt{2} + 2\sqrt{2} = (3 + 2)\sqrt{2} = 5\sqrt{2}$
(2) $3\sqrt{3} - \sqrt{12} = 3\sqrt{3} - 2\sqrt{3} = (3 - 2)\sqrt{3} = \sqrt{3}$
(3) $3\sqrt{18} + \sqrt{32} - \sqrt{50} = 3×3\sqrt{2} + 4\sqrt{2} - 5\sqrt{2} = 9\sqrt{2} + 4\sqrt{2} - 5\sqrt{2} = 8\sqrt{2}$
(4) $\sqrt{27} - \sqrt{12} + \sqrt{\dfrac{1}{3}} = 3\sqrt{3} - 2\sqrt{3} + \dfrac{\sqrt{3}}{3} = (3 - 2 + \dfrac{1}{3})\sqrt{3} = \dfrac{4\sqrt{3}}{3}$
(5) $3\sqrt{40} - \sqrt{\dfrac{2}{5}} - 2\sqrt{\dfrac{1}{10}} = 3×2\sqrt{10} - \dfrac{\sqrt{10}}{5} - 2×\dfrac{\sqrt{10}}{10} = 6\sqrt{10} - \dfrac{\sqrt{10}}{5} - \dfrac{\sqrt{10}}{5} = \dfrac{30\sqrt{10} - \sqrt{10} - \sqrt{10}}{5} = \dfrac{28\sqrt{10}}{5}$
(6) $\sqrt{0.5} - \sqrt{3.2} - 2\sqrt{0.125} + \sqrt{20} = \dfrac{\sqrt{2}}{2} - \dfrac{4\sqrt{5}}{5} - 2×\dfrac{\sqrt{2}}{4} + 2\sqrt{5} = \dfrac{\sqrt{2}}{2} - \dfrac{4\sqrt{5}}{5} - \dfrac{\sqrt{2}}{2} + 2\sqrt{5} = (\dfrac{\sqrt{2}}{2} - \dfrac{\sqrt{2}}{2}) + (-\dfrac{4\sqrt{5}}{5} + \dfrac{10\sqrt{5}}{5}) = \dfrac{6\sqrt{5}}{5}$
2. 计算：
(1) $ 5\sqrt{\dfrac{x}{5}} + \dfrac{5}{2}\sqrt{\dfrac{4x}{5}} - x\sqrt{\dfrac{20}{x}} $； (2) $ \dfrac{2}{3}\sqrt{9x} + 6\sqrt{\dfrac{x}{4}} - 2x\sqrt{\dfrac{1}{2x}} $；
(3) $ \dfrac{3}{2}\sqrt{16x} - (15\sqrt{\dfrac{x}{25}} - 2\sqrt{x^{2}}) $； (4) $ \dfrac{2}{3}x\sqrt{18x} + 12x\sqrt{\dfrac{x}{8}} - x^{3}\sqrt{\dfrac{2}{x^{3}}} $；
(5) $ 2a\sqrt{3ab^{2}} + \dfrac{b}{6}\sqrt{27a^{3}} + 2ab\sqrt{\dfrac{3}{4}a}(b ≥ 0) $；
(6) $ 2\sqrt{a} - 3\sqrt{a^{2}b} + 5\sqrt{4a} - 2b\sqrt{\dfrac{a^{2}}{b}} $。
答案：2. (1) $ 0 $ (2) $ 5\sqrt{x}-\sqrt{2x} $ (3) $ 3\sqrt{x}+2x $ (4) $ 4x\sqrt{2x} $ (5) $ \frac{7}{2}ab\sqrt{3a} $ (6) $ 12\sqrt{a}-5a\sqrt{b} $
解析：
(1) $5\sqrt{\dfrac{x}{5}} + \dfrac{5}{2}\sqrt{\dfrac{4x}{5}} - x\sqrt{\dfrac{20}{x}}$
$=5×\dfrac{\sqrt{5x}}{5} + \dfrac{5}{2}×\dfrac{2\sqrt{5x}}{5} - x×\dfrac{2\sqrt{5x}}{x}$
$=\sqrt{5x} + \sqrt{5x} - 2\sqrt{5x}$
$=0$
(2) $\dfrac{2}{3}\sqrt{9x} + 6\sqrt{\dfrac{x}{4}} - 2x\sqrt{\dfrac{1}{2x}}$
$=\dfrac{2}{3}×3\sqrt{x} + 6×\dfrac{\sqrt{x}}{2} - 2x×\dfrac{\sqrt{2x}}{2x}$
$=2\sqrt{x} + 3\sqrt{x} - \sqrt{2x}$
$=5\sqrt{x} - \sqrt{2x}$
(3) $\dfrac{3}{2}\sqrt{16x} - (15\sqrt{\dfrac{x}{25}} - 2\sqrt{x^{2}})$
$=\dfrac{3}{2}×4\sqrt{x} - (15×\dfrac{\sqrt{x}}{5} - 2|x|)$
$=6\sqrt{x} - (3\sqrt{x} - 2x)$（因为根号下$x$有意义，所以$x≥0$，$|x|=x$）
$=6\sqrt{x} - 3\sqrt{x} + 2x$
$=3\sqrt{x} + 2x$
(4) $\dfrac{2}{3}x\sqrt{18x} + 12x\sqrt{\dfrac{x}{8}} - x^{3}\sqrt{\dfrac{2}{x^{3}}}$
$=\dfrac{2}{3}x×3\sqrt{2x} + 12x×\dfrac{\sqrt{2x}}{4} - x^{3}×\dfrac{\sqrt{2x}}{x^{2}}$
$=2x\sqrt{2x} + 3x\sqrt{2x} - x\sqrt{2x}$
$=4x\sqrt{2x}$
(5) $2a\sqrt{3ab^{2}} + \dfrac{b}{6}\sqrt{27a^{3}} + 2ab\sqrt{\dfrac{3}{4}a}(b ≥ 0)$
$=2a× b\sqrt{3a} + \dfrac{b}{6}×3a\sqrt{3a} + 2ab×\dfrac{\sqrt{3a}}{2}$
$=2ab\sqrt{3a} + \dfrac{1}{2}ab\sqrt{3a} + ab\sqrt{3a}$
$=\dfrac{7}{2}ab\sqrt{3a}$
(6) $2\sqrt{a} - 3\sqrt{a^{2}b} + 5\sqrt{4a} - 2b\sqrt{\dfrac{a^{2}}{b}}$
$=2\sqrt{a} - 3a\sqrt{b} + 5×2\sqrt{a} - 2b×\dfrac{a}{\sqrt{b}}$
$=2\sqrt{a} - 3a\sqrt{b} + 10\sqrt{a} - 2a\sqrt{b}$
$=12\sqrt{a} - 5a\sqrt{b}$
