y * 7 * 8/12 * 56 = 3/4

y = 3/4 chia 56 chia 8/12 chia 7

 y = 9/3136

mk làm cho bn thì bn cug ko **** cho mk 

Ap dụng tính chất DTSBN ta có

\(\frac{x}{9}=\frac{y}{3}=\frac{z}{8}=\frac{x-y+x}{9-3+8}=\frac{56}{14}=4\)

\(+\frac{x}{9}=4=>x=36\)

\(+\frac{y}{3}=4=>y=12\)

\(+\frac{z}{8}=4=>z=32\)

Áp dụng t/c của dãy tỉ số bằng nhau, ta có

 \(\frac{x}{9}=\frac{y}{3}=\frac{z}{8}=\frac{x-y+z}{9-3+8}=\frac{56}{14}=4\)

=> \(\hept{\begin{cases}\frac{x}{9}=4\\\frac{y}{3}=4\\\frac{z}{8}=4\end{cases}}\) => \(\hept{\begin{cases}x=4.9=36\\y=4.3=12\\z=4.8=32\end{cases}}\)

Vậy ....

cảm ơn mấy bạn!

Ta có:
\(\frac{y}{4}=\frac{x}{3}=\frac{x-y}{3-4}=\frac{7}{-1}=-7\)

=> y = (-7). 4 = -28
x = (-7) . 3 = -21

a) y = \(\frac{4}{5}-\frac{3}{4}\)

\(\Rightarrow y=\frac{16}{20}-\frac{15}{20}\)

\(\Rightarrow y=\frac{1}{20}\)

b)\(\frac{y}{7}=\frac{7}{8}-\frac{25}{26}\)

\(\Rightarrow\frac{y}{7}=-\frac{9}{104}\)

\(\Rightarrow y=\frac{-9}{104}.7\)

\(\Rightarrow y=\frac{-63}{104}\)

c) y \(+\frac{7}{12}=\frac{17}{18}-\frac{1}{9}\)

\(\Rightarrow y+\frac{7}{12}=\frac{15}{18}=\frac{5}{6}\)

\(\Rightarrow y=\frac{5}{6}-\frac{7}{12}\)

\(\Rightarrow y=\frac{3}{12}=\frac{1}{4}\)

d)\(y=\frac{7}{8}:\frac{3}{5}=\frac{7}{8}.\frac{5}{3}=\frac{35}{24}\)

e)\(y:4,5=\frac{1}{2}:\frac{6}{5}\)

\(\Rightarrow y:\frac{9}{2}=\frac{1}{2}.\frac{5}{6}=\frac{5}{12}\)

\(\Rightarrow y=\frac{5}{12}.\frac{9}{2}=\frac{15}{8}\)

là 12 đó

k nha

chúc bạn học giỏi

theo mình là 174/7 

k mình nha

Theo đb ta đc:

y+y*1/3+2/7=58

y*(1+1/3)=58-2/7

y*4/3=404/7

y=404/7:4/3

y=303/7

y*4+y*3=644

y*7=644

y         =644/7

y         =92