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電子課本網(wǎng) 第134頁

第134頁

信息發(fā)布者:
$?9\sqrt{2}?$
$解:原式?=3\sqrt{6}+2\sqrt{6}-9×\frac {\sqrt{6}}{18}?$
$?=3\sqrt{6}+2\sqrt{6}-\frac {\sqrt{6}}{2}?$
$?=\frac {9\sqrt{6}}{2}$
$解:原式?=10x2\sqrt{xy}×(5÷15)×\sqrt{\frac {y}{x}÷\frac {x}{y}}?$
$?=10x2\sqrt{xy}×\frac {1}{3}×\frac {y}{x}?$
$?=\frac {10}{3}xy\sqrt{xy}$
$解:原式?=3\sqrt{2}+3\sqrt{5}-2\sqrt{5}-5\sqrt{2}?$
$?=\sqrt{5}-2\sqrt{2}?$
$解:原式?=(4+4\sqrt{10}+10)(14-4\sqrt{10})?$
$?=(14+4\sqrt{10})×(14-4\sqrt{10})?$
$?=142-(4\sqrt{10})2?$
$?=196-160?$
$?=36?$
$解:原式?=\frac {1+x+1-x}{x+1}×\frac {(x+1)2}{2(x-1)}?$
$?=\frac {2}{x+1}×\frac {(x+1)2}{2(x-1)}?$
$?=\frac {x+1}{x-1}?$
$將?x=\sqrt{2}+1?代入原式$
$原式?=\frac {\sqrt{2}+1+1}{\sqrt{2}+1-1}=1+\sqrt{2}$
$解:三角形的面積?=\frac {1}{2}×(3-\sqrt{2})×(3+\sqrt{2})=\frac {7}{2}{cm}^2;?$
$三角形的斜邊長?=\sqrt{{(3-\sqrt{2})}^2+{(3+\sqrt{2})}^2}=\sqrt{22},?$
$∴三角形的周長?=(3-\sqrt{2})+(3+\sqrt{2})+\sqrt{22}=(6+\sqrt{22})\ \mathrm {cm}.?$

$解:?(1)?如圖①所示:$
$?AC+CE=\sqrt{{x}^2+25}+\sqrt{{x}^2-16x+65},?$
$當?A、??C、??E?在同一直線上,?AC+CE?最?。?
$?(2)?作點?N?關于?x?軸的對稱點?N',?連接?MN'?交?x?軸于點?P,?此時?PM+PN?的值最小,等于?MN',?$
$過點?M?作?y?軸的垂線交射線?N'N?于點?A,?如圖②所示.$
$?∵N(3,??2),?$
$?∴N'(3,??-2).?$
$設直線?MN'?得解析式為?y=kx+b,?$
$則?\{\begin{array}{l}{b=4}\\{3k+b=-2}\end{array},?$
$解得?\{\begin{array}{l}{k=-2}\\{b=4}\end{array}.?$
$?∴y=-2x+4.?$
$當?-2x+4=0?時,?x=2,?$
$?∴P(2,??0).?$
$在?Rt△AMN'?中,?AM=3,??AN'=6,?$
$?∴MN'=\sqrt{A{M}^2+AN{'}^2}=\sqrt{{3}^2+{6}^2}=3\sqrt{5}.?$
$?∴PM+PN?最小值為?3\sqrt{5}.?$