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電子課本網(wǎng) › 第103頁

第103頁

信息發(fā)布者：
解：原式??$=(1÷3)×\sqrt {30÷\frac 85}×\frac 23\sqrt {\frac {20}3}$??
??$=\frac 13\sqrt {\frac {75}4}×\frac 23\sqrt {\frac {20}3}$??
??$=(\frac 13×\frac 23)×\sqrt {\frac {75}4×\frac {20}3}$??
??$=\frac 29\sqrt {125}$??
??$=\frac {10}9\sqrt 5$??
解：原式??$=\frac 2b \sqrt {ab^5} ×\frac 13 ×\sqrt {\frac ab}×(-\frac 23\sqrt {a^2b})$??
??$=2b\sqrt {ab}×(-\frac 29a\sqrt a)$??
??$=-\frac {4a^2b}9 \sqrt b$??
解：原式??$=\frac {\sqrt {x-2}}{x-2}×\frac {x^2(x-2)}{\sqrt x}=x \sqrt {x^2-2x}，$??
由二次根式的意義，知??$x> 2，$??
答案不唯一，如取??$x=3，$??
則原式??$=3 \sqrt 3$??
??$ \sqrt n+\sqrt {n-1}$??
解：原式??$=\sqrt 2-1+\sqrt 3-\sqrt 2+...+\sqrt {99}-\sqrt {98}+\sqrt {100}-\sqrt {99}$??
??$ =\sqrt {100}-1$??
??$ =9$??
解： ∵?$x y=4，$??$ x+y=-6$?
∴?$x<0，$??$ y<0$?
∴?$\sqrt {\frac {\overset{}y}x}+\sqrt {\frac xy}$?
?$ =\frac {\sqrt {-y}}{\sqrt {-x}}+\frac {\sqrt {-x}}{\sqrt {-y}}$?
?$ =\frac {\sqrt {x y}}{-x}+\frac {\sqrt {x y}}{-y}$?
?$ = \frac {-(x+y) \sqrt {x y}}{x y}$?
?$ =\frac {-(-6) ×\sqrt 4}4$?
?$ =3$?
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