Bài 9:

Ta có: \(\dfrac{12}{-6}=\dfrac{x}{5}=\dfrac{-y}{3}=\dfrac{z}{-17}=\dfrac{-t}{-9}\)

\(\Leftrightarrow\dfrac{x}{5}=\dfrac{-y}{3}=\dfrac{-z}{17}=\dfrac{t}{9}=-2\)

\(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{x}{5}=-2\\\dfrac{-y}{3}=-2\\\dfrac{-z}{17}=-2\\\dfrac{t}{9}=-2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-10\\-y=-6\\-z=-34\\t=-18\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-10\\y=6\\z=34\\t=-18\end{matrix}\right.\)

Vậy: (x,y,z,t)=(-10;6;34;-18)

Bài 11:

Ta có: \(\dfrac{-7}{6}=\dfrac{x}{18}=\dfrac{-98}{y}=\dfrac{-14}{z}=\dfrac{t}{102}=\dfrac{u}{-78}\)

\(\Leftrightarrow\dfrac{x}{18}=\dfrac{-98}{y}=\dfrac{-14}{z}=\dfrac{t}{102}=\dfrac{u}{-78}=\dfrac{-7}{6}\)

Ta có: \(\dfrac{x}{18}=\dfrac{-7}{6}\)

\(\Leftrightarrow x=\dfrac{18\cdot\left(-7\right)}{6}=-21\)

Ta có: \(\dfrac{-98}{y}=\dfrac{-7}{6}\)

\(\Leftrightarrow y=\dfrac{-98\cdot6}{-7}=84\)

Ta có: \(\dfrac{-14}{z}=\dfrac{-7}{6}\)

\(\Leftrightarrow z=\dfrac{-14\cdot6}{-7}=12\)

Ta có: \(\dfrac{u}{-78}=\dfrac{-7}{6}\)

\(\Leftrightarrow u=\dfrac{-78\cdot\left(-7\right)}{6}=\dfrac{78\cdot7}{6}=91\)

Ta có: \(\dfrac{t}{102}=\dfrac{-7}{6}\)

\(\Leftrightarrow t=\dfrac{-7\cdot102}{6}=-7\cdot17=-119\)

Vậy: (x,y,z,t,u)=(-21;84;12;-119;91)

Nguyễn Lê Phước Thịnh giải giùm mk bài 10 đc ko ạ

-6 /12 = x /8 = -7 /y = z /-18

=>-6*8=12*x

-48=12*x

-48:12=x

=>x=-4

thayx:-6 /12=-4/8=-7/y=z/-18

=>-4*y=8*7

-4*y=56

y=56:(-4)

y=14

=>y=14

thayy:-6/12=-4/8=-7/14=z/18

-4*18=8*z

-72=8*z

-72:8=z

-9=z

=>z=-9

vayx=-4;y=14;z=-9

Làm r nhé,kéo xuống dưới mà xem

khong biet lam

Giải:

Theo đề ra, ta có:

\(\dfrac{x}{8}=-\dfrac{7}{y}=\dfrac{z}{-18}=\dfrac{16}{t}=-\dfrac{6}{12}\)

\(\Leftrightarrow\dfrac{x}{8}=-\dfrac{7}{y}=-\dfrac{z}{18}=\dfrac{16}{t}=-\dfrac{1}{2}\)

\(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{x}{8}=-\dfrac{1}{2}\\-\dfrac{7}{y}=-\dfrac{1}{2}\\-\dfrac{z}{18}=-\dfrac{1}{2}\\\dfrac{16}{t}=-\dfrac{1}{2}\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x=-\dfrac{1}{2}.8\\y=-7:\left(-\dfrac{1}{2}\right)\\z=-\dfrac{1}{2}.\left(-18\right)\\t=16:\left(-\dfrac{1}{2}\right)\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x=-4\\y=14\\z=9\\t=-32\end{matrix}\right.\)

Vậy ...

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Ta có : 

\(\frac{-6}{12}=\frac{x}{8}=\frac{-7}{y}=\frac{z}{-18}=\frac{-1}{2}\)

\(\Rightarrow\hept{\begin{cases}\frac{x}{8}=\frac{-1}{2}\Rightarrow x=\left(-4\right)\\\frac{-7}{y}=\frac{-1}{2}\Rightarrow y=14\\\frac{z}{-18}=\frac{-1}{2}\Rightarrow z=9\end{cases}}\)

Vậy ... 

x/6-1/y=1/2 
=> quy đồng vế trái đc: (xy-6)/6y=1/2 => xy - 6 = 3y => y*(x-3)=6 
=> có các trường hợp: 
y=1 => x-3=6 =>x=9
y=2 => x-3=3 =>x=6
y=3 => x-3=2 =>x=5
y=6 => x-3=1 =>x=4
y=-1 => x-3=-6 =>x=-3
y=-2 => x-3=-3 =>x=0
y=-3 => x-3=-2 =>x=1
y=-6 => x-3=-1 =>x=2

x/6-1/y=1/2

=>quy đồng vế trái được:(xy-6)/6y=1/2  =>xy-6=3y=> y*9(x-3)=6

1 lũ NGU