Bài 1: 

\(A=3-\sqrt{5}+\sqrt{5}=3\)

Câu 1:

\(a,=4\sqrt{3}-10\sqrt{3}+8\sqrt{3}=2\sqrt{3}\\ b,=3-\sqrt{5}+\sqrt{5}-1=2\)

Câu 2:

\(a,ĐK:x\ge-2\\ PT\Leftrightarrow4\sqrt{x+2}-3\sqrt{x+2}+\sqrt{x+2}=6\\ \Leftrightarrow\sqrt{x+2}=3\Leftrightarrow x+2=9\Leftrightarrow x=7\left(tm\right)\\ b,\Leftrightarrow\left\{{}\begin{matrix}x+2y=1\\5y=15\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-5\\y=3\end{matrix}\right.\)

Câu 3:

\(b,PTHDGD:2x-3=-x+3\Leftrightarrow x=2\Leftrightarrow y=1\Leftrightarrow A\left(2;1\right)\\ c,\Leftrightarrow A\left(2;1\right)\in\left(d_3\right)\Leftrightarrow2m-6+m=1\Leftrightarrow m=\dfrac{7}{3}\)

25 A

26 D

27 C

28 2 ý cuối giống

29 C

30 D

a d c c&d c d

Bài 18:

a: =>1,2:x=4/3

=>x=9/10

b: =>\(4.5\cdot x=1.5:2.5=\dfrac{3}{5}\)

hay x=2/15

179. 

\(a.\) \(20:12+7:12=\left(20+7\right):12=\dfrac{27}{12}=\dfrac{9}{4}.\)

\(b.\) \(259:15-136:15=\left(259-136\right):15=123:15=\dfrac{123}{15}=\dfrac{41}{5}.\)

180. 

\(a.\) \(1,9:x+1,7:x=2,4.\Leftrightarrow\left(1,9+1,7\right):x=2,4.\Leftrightarrow3,6:x=2,4.\)

\(\Leftrightarrow x=1,5.\)

\(b.\) \(3:x-0,3:x=3,6.\Leftrightarrow\left(3-0,3\right):x=3,6.\Leftrightarrow2,7:x=3,6.\Leftrightarrow x=0,75.\)

\(c.\) \(x\times2,3+x:10=7,56.\Leftrightarrow x\times2,3+x\times\dfrac{1}{10}=7,56.\)

\(\Leftrightarrow x\times2,3+x\times0,1=7,56.\Leftrightarrow x\times\left(2,3+0,1\right)=7,56.\)

\(\Leftrightarrow x\times2,4=7,56.\Leftrightarrow x=3.15.\)

\(d.\) \(x\times3,05-x:100=7,6.\Leftrightarrow x\times3,05-x\times\dfrac{1}{100}=7,6.\)

\(\Leftrightarrow x\times3,05-x\times0,01=7,6.\Leftrightarrow x\times\left(3,05-0,01\right)=7,6.\)

\(\Leftrightarrow x\times3,04=7,6.\Leftrightarrow x=2,5.\)

\(e.\) \(x:0,25+x\times11=1,8.\Leftrightarrow x:\dfrac{1}{4}+x\times11=1,8.\)

\(\Leftrightarrow x\times4+x\times11=1,8.\Leftrightarrow x\times\left(4+11\right)=1,8.\)

\(\Leftrightarrow x\times15=1,8.\Leftrightarrow x=0,12.\)