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1. 化简$2\sqrt {2}+\sqrt {8}-\sqrt {50}$的结果是(
A. 0
B. $-\sqrt {2}$
C. $\sqrt {2}$
D. $4\sqrt {2}-\sqrt {50}$
B
)A. 0
B. $-\sqrt {2}$
C. $\sqrt {2}$
D. $4\sqrt {2}-\sqrt {50}$
答案：
B
2. 化简$\sqrt {-a^{3}}-a\sqrt {-\frac {1}{a}}$得(
A. $(a-1)\sqrt {-a}$
B. $(1-a)\sqrt {-a}$
C. $-(a+1)\sqrt {a}$
D. $(a-1)\sqrt {a}$
B
)A. $(a-1)\sqrt {-a}$
B. $(1-a)\sqrt {-a}$
C. $-(a+1)\sqrt {a}$
D. $(a-1)\sqrt {a}$
答案：
B
3. 如果最简二次根式$\sqrt {4a+3b}$与$\sqrt [b+1]{2a-b+6}$能够合并,那么$a=$
1
,$b=$1
.
答案：
1 1
4. 计算:
(1)$\sqrt {32}+\sqrt {12.5}-\sqrt {1\frac {1}{8}}$; (2)$(\sqrt {12}+5\sqrt {8})×\sqrt {3}$.
(1)$\sqrt {32}+\sqrt {12.5}-\sqrt {1\frac {1}{8}}$; (2)$(\sqrt {12}+5\sqrt {8})×\sqrt {3}$.
答案：
(1)$\frac {23\sqrt {2}}{4}$
(2)$6+10\sqrt {6}$
(1)$\frac {23\sqrt {2}}{4}$
(2)$6+10\sqrt {6}$
5. 先化简,再求值:
$2(a+\sqrt {3})(a-\sqrt {3})-a(a-6)+6$,其中$a=\sqrt {2}-1$.
$2(a+\sqrt {3})(a-\sqrt {3})-a(a-6)+6$,其中$a=\sqrt {2}-1$.
答案：
解:原式$=2a^{2}-6-a^{2}+6a+6=a^{2}+6a$.
当$a=\sqrt {2}-1$时,原式$=(\sqrt {2}-1)^{2}+6(\sqrt {2}-1)=3-2\sqrt {2}+6\sqrt {2}-6=4\sqrt {2}-3$.
当$a=\sqrt {2}-1$时,原式$=(\sqrt {2}-1)^{2}+6(\sqrt {2}-1)=3-2\sqrt {2}+6\sqrt {2}-6=4\sqrt {2}-3$.
6. 已知x,y满足$\sqrt {4x-5y}+\sqrt {x-y+1}=0$,则$\sqrt {xy}-\sqrt {\frac {x}{y}}$的值为(
A. $\frac {5}{2}\sqrt {5}$
B. $\frac {3}{2}\sqrt {5}$
C. $\frac {1}{2}\sqrt {5}$
D. $2-\sqrt {5}$
B
)A. $\frac {5}{2}\sqrt {5}$
B. $\frac {3}{2}\sqrt {5}$
C. $\frac {1}{2}\sqrt {5}$
D. $2-\sqrt {5}$
答案：
B
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