giúp

$\frac{2\sqrt{15}-2\sqrt{10}+\sqrt{6}-3}{2\sqrt{5}-2\sqrt{10}-\sqrt{3}+\sqrt{6}}$

$=\frac{2.\sqrt{3}.\sqrt{5}-2.\sqrt{2}.\sqrt{5}+\sqrt{2}.\sqrt{3}-\sqrt{3}.\sqrt{3}}{2.\sqrt{5}-2.\sqrt{2}.\sqrt{5}-\sqrt{3}+\sqrt{2}.\sqrt{3}}$ 

$=\frac{2\sqrt{5}(\sqrt{3}-\sqrt{2})+\sqrt{3}(\sqrt{2}-\sqrt{3})}{2\sqrt{5}(1-\sqrt{2})-\sqrt{3}(1-\sqrt{2})}$ 

$=\frac{2\sqrt{5}(\sqrt{3}-\sqrt{2})-\sqrt{3}(\sqrt{3}-\sqrt{2})}{2\sqrt{5}(1-\sqrt{2})-\sqrt{3}(1-\sqrt{2})}$ 

$=\frac{(2\sqrt{5}-\sqrt{3})(\sqrt{3}-\sqrt{2})}{(2\sqrt{5}-\sqrt{3})(1-\sqrt{2})}$

$=\frac{\sqrt{3}-\sqrt{2}}{1-\sqrt{2}}$