\(\frac{7}{x}=\frac{y}{21}=\frac{-42}{54}\)

Ta có : \(\frac{-42}{54}=\frac{-42:6}{54:6}=\frac{-7}{9}\)

+) \(\frac{7}{x}=\frac{-7}{9}\)=> 7.9 = (-7).x => (-7).x = 63 => x = -9

+) \(\frac{y}{21}=\frac{-7}{9}\)=> y.9 = 21.(-7) => y.9 = -147 => y = -49/3

Vậy x = 9,y = -49/3

\(\frac{7}{-9}=\frac{-21}{27}=\frac{-42}{54}\)

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ta có:

    \(\frac{7}{x}=\frac{y}{21}=\frac{-42}{54}\)

=> \(\frac{7}{x}=\frac{-42}{54}\Rightarrow x=\frac{7\cdot54}{\left(-42\right)}=-9\)

=> \(\frac{y}{21}=\frac{-42}{54}\Rightarrow y=\frac{21\cdot\left(-42\right)}{54}=-16\frac{1}{3}\)

`A)2/3=x/60`

`=>40/60=x/60`

`=>x=40`

`B)-1/2=y/18`

`=>-9/18=y/18`

`=>y=-9`

`C)3/x=y/35=-36/84`

Mà `-36/84=(-3 xx 12)/(7 xx 12)=-3/7`

`=>3/x=-3/7`

`=>x=-7`

`y/35=-3/7=-15/35`

`=>y=-15`

`D)7/x=y/27=-42/54`

Mà `-42/54=(-7 xx 6)/(9 xx 6)=-7/9`

`=>7/x=-7/9`

`=>x=-9`

`y/27=-7/9=-21/27`

`=>y=-21`

a) Ta có: \(\dfrac{2}{3}=\dfrac{x}{60}\)

\(\Leftrightarrow x=\dfrac{2\cdot60}{3}=40\)

Vậy: x=40

\(\dfrac{4}{x}=\dfrac{y}{21}=\dfrac{28}{49}=\dfrac{28:7}{49:7}=\dfrac{4}{9}\\ Vậy:x=\dfrac{4.9}{4}=9\\ y=\dfrac{4.21}{9}=\dfrac{28}{3}\)

\(\dfrac{x}{2}=\dfrac{3}{y}\\ \Leftrightarrow x.y=2.3=6\\ Vậy:\left[{}\begin{matrix}\left(x;y\right)=\left(1;6\right)=\left(6;1\right)\\\left(x;y\right)=\left(2;3\right)=\left(3;2\right)\end{matrix}\right.\)

\(3,\\ \dfrac{42}{54}=\dfrac{42:6}{54:6}=\dfrac{7}{9}\\ \dfrac{42}{54}=\dfrac{7}{x}=\dfrac{7}{9}\\ Vậy:x=\dfrac{7.9}{7}=9\)

7/x=y/27=-42/54=-7/9

7/x=-7/9 nên x=-9

y/27=-7/9=-21/27 nên y=-21

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\(\frac{7}{x}=\frac{y}{27}=\frac{-42}{54}\)

+) => \(\frac{y\cdot2}{27\cdot2}=\frac{-42}{54}\)

=> \(y\cdot2=-42\)

\(\Rightarrow y=-21\)

+) \(\frac{7}{x}=\frac{-21}{27}\)

=> \(\frac{7\cdot\left(-3\right)}{x\cdot\left(-3\right)}=\frac{-21}{27}\)

=> \(x\cdot\left(-3\right)=27\)

=> \(x=-9\)

* Lớp 6 chưa học đến tỉ lệ thức nên đây là cách đơn giản nhất r *

\(\frac{y}{27}\)=\(\frac{-42}{54}\)=>\(\frac{2y}{54}\)=\(\frac{-42}{54}\)=>2y= -42                                                                                                                                                                                                                   y= \(\frac{-42}{2}\)= -21                                                                                                                           \(\frac{7}{x}\)=\(\frac{-21}{27}\)=> -21x=7*27=189                                                                                                                                                                                                     x=\(\frac{189}{-21}\)= -9                                                                                                                                                              Vậy x= -9, y= -21

a: =>x/-3=3

hay x=-9

b: =>x/9=-1/9

hay x=-1

c: =>x+1/5=-1/3

hay x=-8/15

d: =>-7/x=-7/9

hay x=9

a, \(\dfrac{x}{-3}=3\Leftrightarrow x=-9\)

b, \(\dfrac{x}{9}=-\dfrac{1}{9}\Rightarrow x=-1\)

c, \(\dfrac{x+3}{15}=-\dfrac{6}{15}\Rightarrow x=-9\)

d, \(\dfrac{42}{-54}=-\dfrac{42}{6x}\Rightarrow6x=54\Leftrightarrow x=9\)