1. -2x=5y =>\(\frac{x}{y}=\frac{-5}{2}=>y=\frac{-2x}{5}\)

Thế y=\(\frac{-2x}{5}\) ta được:

x+\(\frac{-2x}{5}\)=30     \(\Rightarrow\frac{5x-2x}{5}=30\)

\(\Rightarrow3x=150\)\(\Rightarrow x=50\)

=>y=30-x=30-50=-20.

Vậy x=50; y=-20.

Những bài khác tương tự bạn nhé!

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a)

\(\dfrac{x}{5}=\dfrac{y}{2}=\dfrac{3x-2y}{3.5-2.2}=\dfrac{-55}{11}=-5\)

=> \(\left\{{}\begin{matrix}x=-5.5=-25\\y=-5.2=-10\end{matrix}\right.\)

b)

\(\dfrac{x}{3}=\dfrac{y}{2}=\dfrac{2x+5y}{2.3+5.2}=\dfrac{48}{16}=3\)

=> \(\left\{{}\begin{matrix}x=3.3=9\\y=3.2=6\end{matrix}\right.\)

c)

Có: \(\dfrac{x}{y}=-\dfrac{5}{2}\Leftrightarrow-\dfrac{x}{5}=\dfrac{y}{2}=\dfrac{x+y}{-5+2}=\dfrac{30}{-3}=-10\)

=> \(\left\{{}\begin{matrix}x=-10.-5=50\\y=-10.2=-20\end{matrix}\right.\)

d)

Có: \(\dfrac{x}{y}=\dfrac{4}{3}\Leftrightarrow\dfrac{x}{4}=\dfrac{y}{3}=\dfrac{2x+3y}{2.4+3.3}=\dfrac{34}{17}=2\)

=> \(\left\{{}\begin{matrix}x=2.4=8\\y=2.3=6\end{matrix}\right.\)

\(2x=3y\text{⇒}\dfrac{x}{3}=\dfrac{y}{2}\text{⇒}\dfrac{x}{21}=\dfrac{y}{14}\)

\(5y=7z\text{⇒}\dfrac{y}{7}=\dfrac{z}{5}\text{⇒}\dfrac{y}{14}=\dfrac{z}{10}\)

⇒\(\dfrac{x}{21}=\dfrac{y}{14}=\dfrac{z}{10}\)⇒\(\dfrac{3x}{63}=\dfrac{7y}{98}=\dfrac{5z}{50}\)

Áp dụng tính chất dãy tỉ số bằng nhau, ta có:

\(\dfrac{3x}{63}=\dfrac{7y}{98}=\dfrac{5z}{50}=\dfrac{3x-7y+5z}{63-98+50}=\dfrac{30}{15}=2\)

⇒x=42,y=28,z=20

\(\dfrac{x}{3}=\dfrac{y}{2}\)⇒\(\dfrac{x}{15}=\dfrac{y}{10}\)

\(\dfrac{x}{5}=\dfrac{z}{7}\text{⇒}\dfrac{x}{15}=\dfrac{z}{21}\)

⇒\(\dfrac{x}{15}=\dfrac{y}{10}=\dfrac{z}{21}\)⇒\(\dfrac{x}{15}=\dfrac{2y}{20}\)

Áp dụng tính chất dãy tỉ số bằng nhau ta có:

\(\dfrac{x}{15}=\dfrac{2y}{20}=\dfrac{x+2y}{15+20}=\dfrac{-112}{35}=\dfrac{-16}{5}\)

⇒x=48,y=32,z=336/5

Lời giải:

1. Áp dụng tính chất dãy tỉ số bằng nhau:

$\frac{x}{3}=\frac{y}{2}=\frac{2y}{4}=\frac{x+2y}{3+4}=\frac{-112}{7}=-16$

$\Rightarrow x=-16.3=-48; y=-16.2=-32$

Đoạn $\frac{x}{5}=\frac{x}{7}$ là sao em? Em xem lại đề.

2. 

$2x=3y\Rightarrow \frac{x}{3}=\frac{y}{2}\Rightarrow \frac{x}{21}=\frac{y}{14}(1)$

$5y=7z\Rightarrow \frac{y}{7}=\frac{z}{5}\Rightarrow \frac{y}{14}=\frac{z}{10}(2)$

Từ $(1);(2)\Rightarrow \frac{x}{21}=\frac{y}{14}=\frac{z}{10}$

Áp dụng tính chất dãy tỷ số bằng nhau:

$\frac{x}{21}=\frac{y}{14}=\frac{z}{10}$

$=\frac{3x}{63}=\frac{7y}{98}=\frac{5z}{50}=\frac{3x-7y+5z}{63-98+50}=\frac{30}{15}=2$

$\Rightarrow x=2.21=42; y=2.14=28; z=2.10=20$

1.A.0.96

Câu a tự làm nhé

b, \(\frac{2x+3}{24}=\frac{3x-1}{32}\)

\(\Leftrightarrow32(2x+3)=24(3x-1)\)

\(\Leftrightarrow64x+96=72x-24\)

\(\Leftrightarrow64x+96-72x=-24\)

\(\Leftrightarrow96-8x=-24\Leftrightarrow x=15\)

2. a. \(\frac{x}{3}=\frac{y}{4}=\frac{z}{6}\) và x + y + z = 52

Ta có : \(\frac{x}{3}=\frac{y}{4}=\frac{z}{6}=\frac{x+y+z}{3+4+6}=\frac{52}{13}=4\)\((\)áp dụng tính chất dãy tỉ số bằng nhau \()\)

Vậy : \(\hept{\begin{cases}\frac{x}{3}=4\\\frac{y}{4}=4\\\frac{z}{6}=4\end{cases}}\Leftrightarrow\hept{\begin{cases}x=12\\y=16\\z=24\end{cases}}\)

\(\hept{\begin{cases}3x=2y\\2x+y=3\end{cases}\Leftrightarrow\hept{\begin{cases}y=\frac{3}{2}.x\\2x+\frac{3}{2}.x=3\end{cases}\Leftrightarrow}\hept{\begin{cases}y=\frac{3}{2}.x\\\frac{7}{2}.x=3\end{cases}\Leftrightarrow}\hept{\begin{cases}x=\frac{6}{7}\\y=\frac{9}{7}\end{cases}}}\)

\(\hept{\begin{cases}\frac{x}{3}=\frac{3y}{4}\\3x-y=4\end{cases}\Leftrightarrow\hept{\begin{cases}4x=9y\\3x-y=4\end{cases}\Leftrightarrow}\hept{\begin{cases}x=\frac{9y}{4}\\\frac{3.9}{4}y-y=4\end{cases}\Leftrightarrow}\hept{\begin{cases}x=\frac{9}{4}.y\\\frac{23}{4}.y=4\end{cases}\Leftrightarrow}\hept{\begin{cases}x=\frac{9}{4}.y\\y=\frac{16}{23}\end{cases}\Leftrightarrow}\hept{\begin{cases}x=\frac{36}{23}\\y=\frac{16}{23}\end{cases}}}\)

Các phần sau làm tương tự nhé