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電子課本網(wǎng) 第135頁

第135頁

信息發(fā)布者:
$\frac{\sqrt {3} }{2} $
$\frac{3\sqrt{10}}{5} $
$ \begin{aligned}解:原式&=-\frac{1}{3}·\sqrt {9y} \\ &= -\sqrt{y}. \\ \end{aligned}$
$ 解:原式 = \sqrt{\frac{2}{45}}÷ \sqrt{(\frac{3}{2})^{2} ×\frac{8}{5}} $
$~~~~~~~~~~~~~~~~= \sqrt{\frac{2}{45}}÷ \sqrt{\frac{18}{5}} $
$~~~~~~~~~~~~~~~~= \sqrt{\frac{2}{45}×\frac{5}{18}}= \frac{1}{9}. $
$解:由題意,,得\begin{cases}{ 2x-5≥0, }\ \\ { 10-4x≥0, } \end{cases}\ $
$解得x=\frac{5}{2},∴y=1.\ $
$∵x \sqrt{2x}÷ \sqrt{\frac{x}{y}}=x \sqrt{2x÷\frac{x}{y}}=x \sqrt{2y},\ $
$∴當(dāng)x=\frac{5}{2},y=1時(shí),原式=\frac{5\sqrt {2} }{2}.$
$解:由題意得\begin{cases}{ 9-x≥0, } \\ {x-6>0, } \end{cases} 解得6<x≤9. $
$ ∵x為偶數(shù),∴x=8, $
$ ∴ (1+x)· \sqrt{\frac{1-2x+x2}{x2-1}}=(1+x) ·\sqrt{\frac{(x-1)2}{(x+1)(x-1)}}$
$= \sqrt{\frac{(x+1)2(x-1)2}{(x+1)(x-1)}}=\sqrt {(x+1)(x-1)}\ $
$=\sqrt {9×7}=3\sqrt {7} .$
$解:設(shè)a= \sqrt{3\sqrt{5\sqrt {3\sqrt {5···}} } },$
$兩邊平方,得a2=3 \sqrt{{5\sqrt {3\sqrt {5···}} }},$
$a?=45 \sqrt{3\sqrt{5···}},$
$則a?=45a.因?yàn)閍≠0,兩邊同除以a,$
$得a3=45,∴a=\sqrt [3]{45} .$
$解:原式= \sqrt{(\frac{a}{2})^{2} ·ab2} ÷ \sqrt{(4a)2·\frac{a}}\ $
$~~~~~~~~~~~~~~~~= \sqrt{\frac{a^{3} b^{2} }{4}} ÷ \sqrt{\frac{16a^{3} }}$
$~~~~~~~~~~~~~~~~= \sqrt{\frac{a^{3} b^{2} }{4}·\frac{16a^{3} }} = \frac{8}\sqrt { b}.\ $
$解:∵x\lt 1,∴y= \frac{ |x-1|}{x-1} +3= \frac{-(x-1)}{x-1} +3=2,$
$∴原式=y·\sqrt {3y}·\sqrt {y^{4} }· \sqrt{\frac{1}{y}} =\sqrt {3} y^{3} ,$
$當(dāng)y=2時(shí),原式=8\sqrt {3} .$
$解:設(shè)x= \sqrt{4+\sqrt{7}} - \sqrt{4-\sqrt {7} } ,$
$兩邊平方,$
$得x2=( \sqrt{4+\sqrt {7} } )2+\ ( \sqrt{4-\sqrt {7} } )2$
$-2 \sqrt{(4+\sqrt {7} )(4-\sqrt {7} )} ,$
$即x2=4+\sqrt {7} +4-\sqrt {7} -6,\ $
$∴x2=2,∴x=±\sqrt {2} .\ $
$∵\(yùn)sqrt{4+\sqrt {7} } - \sqrt{4-\sqrt{7}} > 0.$
$∴. \sqrt{4+\sqrt{7}} - \sqrt{4-7} =\sqrt {2} .$