a: \(\dfrac{1}{3}\cdot\sqrt{72}-3\sqrt{50}-\dfrac{\sqrt{66}}{\sqrt{33}}\)
\(=\dfrac{1}{3}\cdot6\sqrt{2}-3\cdot5\sqrt{2}-\sqrt{2}\)
\(=2\sqrt{2}-15\sqrt{2}-\sqrt{2}=-14\sqrt{2}\)
b: \(2\sqrt{3x}-\sqrt{75x}+\dfrac{1}{2}\cdot\sqrt{48x}\)
\(=2\sqrt{3x}-5\sqrt{3x}+\dfrac{1}{2}\cdot4\sqrt{3x}\)
\(=-3\sqrt{3x}+2\sqrt{3x}=-\sqrt{3x}\)
\(\dfrac{1}{3}\sqrt{72}-3\sqrt{50}-\dfrac{\sqrt{66}}{\sqrt{33}}\\ =\dfrac{1}{3}\sqrt{36\cdot2}-3\sqrt{25\cdot2}-\sqrt{\dfrac{66}{33}}\\ =\dfrac{1}{3}\cdot6\sqrt{2}-3\cdot5\sqrt{2}-\sqrt{2}\\ =2\sqrt{2}-15\sqrt{2}-\sqrt{2}\\ =-14\sqrt{2}\)
\(b,2\sqrt{3x}-\sqrt{75x}+\dfrac{1}{2}\sqrt{48x}\\ =2\sqrt{3x}-\sqrt{25\cdot3x}+\dfrac{1}{2}\sqrt{16\cdot3}\\ =2\sqrt{3x}-5\sqrt{3x}+\dfrac{1}{2}\cdot4\sqrt{3x}\\ =2\sqrt{3x}-5\sqrt{3x}+2\sqrt{3x}\\ =-\sqrt{3x}\)
