1. tính giá trị biểu thức :
a) \(\sqrt{\dfrac{2}{3}}+2\sqrt{\dfrac{3}{2}}-\sqrt{6}\)
b) \(3\sqrt{\dfrac{2}{5}}+\sqrt{\dfrac{5}{2}}-2\sqrt{10}\)
c) \(-\sqrt{\dfrac{3}{5}}+3\sqrt{\dfrac{5}{3}}-4\sqrt{15}\)
d) \(\dfrac{2}{\sqrt{6}-2}+\dfrac{2}{\sqrt{6}+2}+\dfrac{5}{\sqrt{6}}\)