1.计算:
(1)$(\sqrt {18}-\sqrt {8})×\sqrt {2}$;
(2)$\sqrt {6}×\sqrt {2}+\sqrt {24}÷\sqrt {3}-|-2\sqrt {3}|$;
(3)$\sqrt {48}÷\sqrt {3}-\sqrt {\frac {1}{2}}×\sqrt {12}+\sqrt {24}$;
(4)$\sqrt {18}-4\sqrt {\frac {1}{2}}+\sqrt {24}÷\sqrt {3}$.

(1)2 (2)$2\sqrt {2}$ (3)$4+\sqrt {6}$ (4)$3\sqrt {2}$

2.计算:
(1)$(\sqrt {12}-\sqrt {8})×\sqrt {6}-\sqrt {72}$;
(2)$(2\sqrt {12}-\sqrt {3}+\sqrt {27})×\sqrt {3}$;
(3)$(\sqrt {12}+\frac {1}{4}\sqrt {48}-9\sqrt {\frac {1}{3}})÷\sqrt {18}$;
(4)$(10\sqrt {48}-6\sqrt {27}+4\sqrt {12})÷\sqrt {6}$.

(1)$-4\sqrt {3}$ (2)18 (3)0 (4)$15\sqrt {2}$

3.计算:
(1)$\frac {\sqrt {32}-\sqrt {8}}{\sqrt {2}}$;
(2)$\frac {\sqrt {40}+\sqrt {5}}{\sqrt {5}}-\sqrt {24}×\sqrt {\frac {1}{2}}$;
(3)$\frac {x-y}{\sqrt {x}+\sqrt {y}}$;
(4)$\frac {x-2+\sqrt {x^{2}-4}}{x+2+\sqrt {x^{2}-4}}(x＞2)$.

(1)2 (2)$2\sqrt {2}+1-2\sqrt {3}$ (3)$\sqrt {x}-\sqrt {y}$ (4)$\frac {\sqrt {x^{2}-4}}{x+2}$