\(\frac{-5}{x}=\frac{-y}{8}=\frac{18}{72}\)

\(\Leftrightarrow\frac{-5}{x}=\frac{-y}{8}=\frac{1}{4}\)

\(\Leftrightarrow\orbr{\begin{cases}-\frac{5}{x}=\frac{1}{4}\\-\frac{y}{8}=\frac{1}{4}\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=-5.4:1\\-y=8.1:4\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-20\\-y=2\end{cases}\Leftrightarrow}\orbr{\begin{cases}x=-20\\y=-2\end{cases}}}\)

vậy x=-20 và y=-2

\(-\frac{1}{3}-x=\frac{1}{2}-\frac{1}{-4}\)

\(-\frac{1}{3}-x=\frac{1}{2}-\frac{-1}{4}\)

\(-\frac{1}{3}-x=\frac{2}{4}-\frac{-1}{4}\)

\(-\frac{1}{3}-x=\frac{3}{4}\)

\(x=-\frac{1}{3}-\frac{3}{4}\)

\(x=-\frac{4}{12}-\frac{9}{12}\)

\(x=-\frac{13}{12}\)

\(x=-\frac{18}{24}+\frac{15}{21}\)

\(x=-\frac{3}{4}+\frac{5}{7}\)

\(x=-\frac{21}{28}+\frac{20}{28}\)

\(x=-\frac{1}{28}\)

Ta có : 

         -5/x = -18/72 

=> -5 . 72 = -18 . x 

=> -360    = -18 . x 

=>    x      = -360 :- 18

=>    x      = 20  

Thay x = 20 ta được : 

       -5/20 = y/16 

=> -5 . 16 = 20 . y  

=>    -80   = 20 . y 

=>      y    = -80 : 20

=>      y    = -4

Vậy x = 20 , y = -4

Chúc bạn học giỏi nha !!! 
Dấu " / " là chia 

TK mình nha !!! ^_^ 

x = 45/2                            y = -32/9

x=20

y=-4

Hok tốt

^_^

Xét \(\frac{-5}{x}=\frac{-18}{72}\)

\(\Rightarrow\)(-5) . 72 = x . (-18)

\(\Rightarrow\)-360 = x . (-18)

\(\Rightarrow\)x = (-360) : (-18) = 20

Xét \(\frac{y}{16}=\frac{-18}{72}\)

\(\Rightarrow\)72y = 16 . (-18)

\(\Rightarrow\)72y = -288

\(\Rightarrow\)y = (-288) : 72 = -4

Vậy x = 20 ; y = -4

Ta có : 

   \(\frac{-5}{x}=\frac{-18}{72}\Rightarrow\frac{-5}{x}=\frac{-1}{4}\)  

                            \(\Rightarrow-5.4=x.-1\) 

                            \(\Rightarrow-20=-x\)

                            \(\Rightarrow x=20\)

Thay x = 20 vào  \(\frac{-5}{x}\)ta được : 

\(\frac{-5}{20}=\frac{y}{16}\)\(\Rightarrow\frac{-1}{4}=\frac{y}{16}\Rightarrow-1.16=y.4\)

                                                   \(\Rightarrow-16=y.4\)  

                                                    \(\Rightarrow y=-4\)  

Vậy x = 20 , y = -4

Tk mk nha !!! 

-18/72=-2/8=-4/16. Suy ra x=-4 

-5/x=-2/8.Suy ra -5.8=-2.x

-40=-2x

x=20

xem lại đề

-18.16=72.y ( nhân chéo )

-288=72.y

y=-4

-5.16=-4(thay vào y) .x

-80=-4.x

x=20

\(\frac{72-x}{3}=\frac{x-18}{5}\)

\(\Rightarrow\frac{\left(72-x\right).5}{15}=\frac{3\left(x-18\right)}{15}\)

\(\Rightarrow\left(72-x\right).5=3\left(x-18\right)\)

\(\Rightarrow360-5x=3x-54\)

\(\Rightarrow-3x-5x=-360-54\)

\(\Rightarrow-8x=-414\)

\(\Rightarrow x=51,75\)

+) Vì \(\frac{72-x}{3}=\frac{x-18}{5}\)

\(\Rightarrow5\left(72-x\right)=3\left(x-18\right)\)

     \(5.72-5x=3x-3.18\)

      \(360-5x=3x-54\)

       \(-5x-3x=-54-360\)

       \(-8x=-414\)

              \(x=-414:\left(-8\right)\)

              \(x=51,75\)

      Vậy x = 51,75

\(\frac{72-x}{3}=\frac{x-18}{5}\)

\(\Leftrightarrow5\left(7x-2\right)=3\left(x-18\right)\)

\(\Leftrightarrow360-5x=3x-54\)

\(\Leftrightarrow360=3x-54+5x\)

\(\Leftrightarrow360=8x-54\)

\(\Leftrightarrow8x-54=360\) (chuyển vế)

\(\Leftrightarrow8x=360+54\)

\(\Leftrightarrow8x=414\)

\(\Leftrightarrow x=\frac{414}{8}=\frac{207}{4}\)

\(\Rightarrow x=\frac{207}{4}\)