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第24頁

信息發(fā)布者：

解?$：(1) 4 x^2=1 $?

?$x ^2=\frac {1}{4} $?

?${x}= \pm \sqrt {\frac {1}{4}} $?

?${x}= \pm \frac {1}{2} $?

?$(2) 15^2+x^2=17^2 $?

?$x^2=17^2-15^2 $?

?$x^2=64 $?

?${x}= \pm \sqrt {64} $?

?${x}= \pm 8$?

解?$：(1)-\sqrt {81}=-9 $?

?$(2) \pm \sqrt {\frac {25}{36}}= \pm \frac {5}{6}$?

?$(3)\sqrt {(-25)^2}-\sqrt {0.09} =\sqrt {625}-\sqrt {0.09} =25-0.3 =24.7$?

解: ∵?$\sqrt {x+2 y-5}+|2 x-y-5|=0， $?

∴?$\begin {cases}{x+2 y-5=0， }\\{2 x-y-5=0，}\end {cases}$?

解得?$ x=3 \text {, } y=1$?

∴?$ x+y=4， $?∴?$x+y $?的平方根是?$ \pm 2 .$?

4225

9025

B

全體實(shí)數(shù)

?$\text {解: (1) } 8 x^{3}+3=-24 $?

?$8 x^3=-27 $?

?$x^3=-\frac {27}{8} $?

?$x=-\frac {3}{2}$?

?$(2) (x-2)^3=-8 $?

?$x-2=-2$?

?$x=0$?

2

解?$：(1)\sqrt [3]{\frac {19}{27}-1}=\sqrt [3]{-\frac {8}{27}}=\sqrt [3]{(-\frac {2}{3})^3}= -\frac {2}{3}$?

?$(2)\sqrt [3]{(-\frac {3}{2})^3}=\sqrt [3]{-\frac {27}{8}}=\sqrt [3]{(-\frac {3}{2})^3}= -\frac {3}{2}$?

?$(3) (\sqrt [3]{64})^3=(\sqrt [3]{4^3})^3=4^3=64 $?

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