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9. (★★)如果$a,b$是有理数,且$\sqrt {4}-\sqrt {18}+\sqrt {\frac {1}{2}}= a+b\sqrt {2}$,则$a+b= $ _ .
答案：
$-\frac{1}{2}$
10. (★★)计算:$(π+1)^{0}-\sqrt {12}+|-\sqrt {3}|= $ _ .
答案：
$1 - \sqrt{3}$
11. (★★)计算二次根式$5\sqrt {a}-3\sqrt {b}-7\sqrt {a}+9\sqrt {b}$的最后结果是 _ .
答案：
$-2\sqrt {a}+6\sqrt {b}$
12. (★★★)已知等腰直角三角形的直角边的长为$\sqrt {2}$,那么这个等腰直角三角形的周长是 _ .
答案：
$2 + 2\sqrt{2}$
13. (★★★)在$\sqrt {8},\frac {1}{3}\sqrt {75a},\frac {2}{3}\sqrt {9a},\sqrt {125},\frac {2}{a}\sqrt {3a^{3}},3\sqrt {0.2},-2\sqrt {\frac {1}{8}}$中,与$\sqrt {3a}$是同类二次根式的有 _ .
答案：
$\frac{1}{3}\sqrt{75a}$，$\frac{2}{a}\sqrt{3a^{3}}$
14. (★★★)已知$a+b= -8,ab= 8$,化简$b\sqrt {\frac {b}{a}}+a\sqrt {\frac {a}{b}}= $ _ .
答案：
$-12\sqrt{2}$
15. (★★)计算:
(1)$3\sqrt {2}+5\sqrt {2}$;
(2)$\sqrt {1\frac {2}{3}}-2\sqrt {45}+2\sqrt {20}$;
(3)$\frac {2}{3}\sqrt {9a}+6\sqrt {\frac {a}{4}}-2a\sqrt {\frac {1}{a}}$;
(4)$(3-\sqrt {3})^{2}+(3+\sqrt {3})^{2}$;
(5)$(\sqrt {6}+\sqrt {8})×\sqrt {3}$;
(6)$(4\sqrt {6}-3\sqrt {2})÷2\sqrt {2}$.
(1)$3\sqrt {2}+5\sqrt {2}$;
(2)$\sqrt {1\frac {2}{3}}-2\sqrt {45}+2\sqrt {20}$;
(3)$\frac {2}{3}\sqrt {9a}+6\sqrt {\frac {a}{4}}-2a\sqrt {\frac {1}{a}}$;
(4)$(3-\sqrt {3})^{2}+(3+\sqrt {3})^{2}$;
(5)$(\sqrt {6}+\sqrt {8})×\sqrt {3}$;
(6)$(4\sqrt {6}-3\sqrt {2})÷2\sqrt {2}$.
答案：
1.$8\sqrt {2}$ 2.$\frac{\sqrt{15}}{3}-2\sqrt{5}$ 3.$3\sqrt{a}$ 4.$24$ 5.$3\sqrt{2}+2\sqrt{6}$ 6.$2\sqrt{3}-\frac{3}{2}$
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