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電子課本網(wǎng) 第5頁(yè)

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信息發(fā)布者:
解:(1) 因?yàn)檎龜?shù)$x$的平方根分別是$a + 3$和$2a-15,$
根據(jù)一個(gè)正數(shù)的兩個(gè)平方根互為相反數(shù),可得:
$(a + 3)+(2a-15)=0$
$a + 3+2a-15=0$
$3a-12 = 0$
$3a=12$
$a = 4$
則$x=(a + 3)^2=(4 + 3)^2=49。$
(2) 因?yàn)?\sqrt{2b-1}=3,$兩邊同時(shí)平方可得$2b-1 = 9,$$2b=10,$$b = 5。$
所以$a + b=4 + 5=9,$$a + b$的算術(shù)平方根為$\sqrt{9}=3。$
C
A
20
6
$\frac{4}{5}$
$\begin{aligned}&\sqrt{12}-\vert1-\sqrt{3}\vert-\pi^0+(\frac{1}{2})^{-1}\\=&2\sqrt{3}-(\sqrt{3}-1)-1 + 2\\=&2\sqrt{3}-\sqrt{3}+1-1 + 2\\=&\sqrt{3}+2\end{aligned}$
$\begin{aligned}&(2\sqrt{2}-\sqrt{3})(2\sqrt{2}+\sqrt{3})-(\sqrt{2})^2\\=&(2\sqrt{2})^2-(\sqrt{3})^2-2\\=&8 - 3-2\\=&3\end{aligned}$
$\begin{aligned}&(\sqrt{5}-2)^2-\sqrt{36}-\vert\sqrt{5}-3\vert\\=&5-4\sqrt{5}+4 - 6-(3-\sqrt{5})\\=&5-4\sqrt{5}+4 - 6-3+\sqrt{5}\\=&(5 + 4-6-3)+(-4\sqrt{5}+\sqrt{5})\\=&0-3\sqrt{5}\\=&-3\sqrt{5}\end{aligned}$
$\begin{aligned}&2\sqrt{12}+3\sqrt{1\frac{1}{3}}-\sqrt{5\frac{1}{3}}-\frac{2}{3}\sqrt{48}\\=&2\times2\sqrt{3}+3\sqrt{\frac{4}{3}}-\sqrt{\frac{16}{3}}-\frac{2}{3}\times4\sqrt{3}\\=&4\sqrt{3}+3\times\frac{2}{\sqrt{3}}-\frac{4}{\sqrt{3}}-\frac{8}{3}\sqrt{3}\\=&4\sqrt{3}+2\sqrt{3}-\frac{4}{\sqrt{3}}-\frac{8}{3}\sqrt{3}\\=&(4 + 2-\frac{8}{3})\sqrt{3}-\frac{4}{\sqrt{3}}\\=&\frac{10}{3}\sqrt{3}-\frac{4\sqrt{3}}{3}\\=&2\sqrt{3}\end{aligned}$