Chọn A

\(a,\dfrac{x}{5}=\dfrac{-18}{10}\\ \Rightarrow x=-\dfrac{18}{10}.5\\ \Rightarrow x=-9\\ b,\dfrac{6}{x-1}=\dfrac{-3}{7}\\ \Rightarrow6.7=-3\left(x-1\right)\\ \Rightarrow42=-3x+3\\ \Rightarrow42+3x-3=0\\ \Rightarrow3x+39=0\\ \Rightarrow3x=-39\\ \Rightarrow x=-13\\ c,\dfrac{y-3}{12}=\dfrac{3}{y-3}\\ \Rightarrow\left(y-3\right)^2=36\\ \Rightarrow\left[{}\begin{matrix}y-2=6\\y-2=-6\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}y=8\\y=-4\end{matrix}\right.\)

\(d,\dfrac{x}{25}=\dfrac{-5}{x^2}\\ \Rightarrow x^3=-125\\ \Rightarrow x^3=\left(-5\right)^3\\ \Rightarrow x=-5\)

\(x:33=\dfrac{9}{66}\)
\(x=\dfrac{9}{66}\times33\)
\(x=\dfrac{9}{2}\)
\(\dfrac{4}{5}\times x=\dfrac{10}{11}:\dfrac{3}{4}\)
\(\dfrac{4}{5}\times x=\dfrac{40}{33}\)
\(x=\dfrac{40}{33}:\dfrac{4}{5}\)
\(x=\dfrac{50}{33}\)
#Đạt Đang Bận Thở

Bài 10:

a: Để A là phân số thì n+2<>0

hay n<>-2

b: Khi n=0 thì A=3/2

Khi n=2 thì A=3/(2+2)=3/4

Khi n=-7 thì A=3/(-7+2)=-3/5

Bài 9:

1)9/x = -35/105               2) 12/5 = 32/x                   3)x/2 = 32/x                            x = 9. (-35)/105              x.12/5 = x.32/x                    2x.x/2 = 2x.32/x        

        x = -3                              x.12/5=32                         xx = 2.32

                                                        x= 32:12/5                x^2 = 2.32

                                                         x = 40/3                   x^2 = 64

                                                                                         x = 8

4) x-2/4 = x-1/5

      5(x-2) = 4(x-1)
       5x - 10 = 4x - 4
        5x - 4x = 10 - 4
         x = 6   

  Bài 10:Cho biểu thức 

a) Ta có: \(\dfrac{x}{3}=\dfrac{7}{25}+\dfrac{-1}{5}\)

\(\Leftrightarrow\dfrac{x}{3}=\dfrac{7}{25}+\dfrac{-5}{25}=\dfrac{2}{25}\)

hay \(x=\dfrac{6}{25}\)

Vậy: \(x=\dfrac{6}{25}\)

b) Ta có: \(\dfrac{4}{9}+\dfrac{x}{5}=\dfrac{5}{11}\)

\(\Leftrightarrow\dfrac{x}{5}=\dfrac{5}{11}-\dfrac{4}{9}=\dfrac{45}{99}-\dfrac{44}{99}=\dfrac{1}{99}\)

hay \(x=\dfrac{5}{99}\)

Vậy: \(x=\dfrac{5}{99}\)

c) Ta có: \(\dfrac{-5}{9}+\dfrac{x}{10}=\dfrac{1}{3}\)

\(\Leftrightarrow\dfrac{x}{10}=\dfrac{1}{3}+\dfrac{5}{9}=\dfrac{3}{9}+\dfrac{5}{9}=\dfrac{8}{9}\)

hay \(x=\dfrac{80}{9}\)

Vậy: \(x=\dfrac{80}{9}\)

1.

=2/5 x 12/3 + 2/5 x 15/3 + 2/5 x 1

= 2/5 x (12/3 + 15/3 + 1)

=2/5 x 1

=2/5

2.a=1;2

Bài 1 : 

\(=\dfrac{2}{11}+\dfrac{4}{11}-\dfrac{6}{11}-\dfrac{3}{8}-\dfrac{5}{8}=0-1=-1\)

Bài 2 : 

\(\Rightarrow3+x=8\Leftrightarrow x=5\)

Bài 3 : 

\(\Leftrightarrow x-\dfrac{5}{11}=\dfrac{5}{4}\Leftrightarrow x=\dfrac{35}{44}\)

Bài 4 : 

Trong 2 ngày An đọc được số quyên phần quyên sách 

\(\dfrac{1}{11}+\dfrac{8}{11}=\dfrac{9}{11}\)( quyển sách ) 

đs : 9/11 quyển sách 

a: =>19/23>19/x>19/29

=>\(x\in\left\{24;25;26;27;28\right\}\)

b: =>88/132<88/x<88/128

=>132>x>128

=>\(x\in\left\{131;130;129\right\}\)

c: =>\(\left\{{}\begin{matrix}\dfrac{4}{x}-\dfrac{x}{8}< 0\\\dfrac{x}{8}-\dfrac{5}{x}< 0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\dfrac{32-x^2}{8x}< 0\\\dfrac{x^2-40}{8x}< 0\end{matrix}\right.\)

=>32<x^2<40

=>x=6