\(4\frac{1}{3}:\frac{x}{4}=\frac{6}{0,3}\)

\(\Rightarrow\frac{13}{3}:\frac{x}{4}=20\)

\(\Rightarrow\frac{x}{4}=\frac{13}{3}:20\)

\(\Rightarrow\frac{x}{4}=\frac{13}{60}\)

\(\Rightarrow x=\frac{13}{60}.4\)

\(\Rightarrow x=\frac{13}{15}\)

\(4\frac{1}{3}:\frac{x}{4}=\frac{6}{0.3}\)

\(\frac{13}{3}:\frac{x}{4}=20\)

\(\frac{x}{4}=\frac{13}{3}:20\)

\(\frac{x}{4}=\frac{13}{60}\)

\(x=\frac{13}{60}.4\)

a/ 3x-5/x+4=5/2

<=> 6x-10=5x+20

<=> 6x-5x=30

<=> x=30

b/ 3x-1/2x+1=3/7

<=> 21x-7 = 6x+3

<=> 21x-6x=10

<=> 15x =10

<=> x=10/15

\(\frac{x}{7}=\frac{18}{14}\)

=>\(x=18.7:14=9\)

=> x=9

\(\frac{x}{7}=\frac{18}{14}\)

\(\Rightarrow x=\frac{18\cdot7}{14}=9\)

9

\(\frac{x}{8}=\frac{x}{x^3}\)

\(\Leftrightarrow\frac{x}{8}=\frac{1}{x^2}\)

\(\Leftrightarrow x\cdot x^2=8\)

\(\Leftrightarrow x^3=8\)

\(\Leftrightarrow x^3=2^3\)

\(\Leftrightarrow x=2\)

Vậy x = 2

Ta co:

\(\frac{x}{8}=\frac{x}{x^3}\Rightarrow x.x^3=x.8\)

\(\Rightarrow x^4=x.8\Rightarrow x^4:x=8\)

\(\Rightarrow x^3=8\Rightarrow x^3=2^3\Rightarrow x=2\)

Vay x=2

2,5 : (3x-5) = 3: (4x-2)

=> (3x-5)(4x-2) =2,5 :  3 

=> 12x^2 - 6x - 20x + 10 - 5/6 = 0

=> 12x^2 - 26x + 55/6 = 0 

a: Hệ số tỉ lệ của y đối với x là:

\(k=\dfrac{y}{x}=\dfrac{10}{50}=\dfrac{1}{5}\)

=>\(y=\dfrac{1}{5}x\)

b: Thay x=20 vào \(y=\dfrac{1}{5}x\), ta được:

\(y=\dfrac{1}{5}\cdot20=4\)

Đặt    \(\frac{x}{4}=\frac{y}{7}=k\)

=>   \(x=4k;\)\(y=7k\)

Ta có:     \(xy=112\)

=>    \(4k.7k=112\)

<=>  \(28k^2=112\)

<=>  \(k^2=4\)

<=>  \(k=\pm2\)

Đến đây bạn thay vào tự tính

Ta có: \(\frac{x}{4}=\frac{y}{7}=k\)

\(\Rightarrow x=4k,y=7k\)

Mà \(xy=112\)

\(\Rightarrow4k.7k=112\)

\(\Rightarrow28k^2=112\)

\(\Rightarrow k^2=112:28\)

\(\Rightarrow k^2=4\)

\(\Rightarrow k^2=2^2\)

\(\Rightarrow k=2\)

\(\Rightarrow\orbr{\begin{cases}x=2.4=8\\y=2.7=14\end{cases}}\)

\(\frac{x}{4}=\frac{y}{7}\Rightarrow\frac{y^2}{49}=\frac{x^2}{16}=\frac{x}{4}\cdot\frac{x}{4}=\frac{x}{4}\cdot\frac{y}{7}\)\(=\frac{xy}{4\cdot7}=\frac{112}{28}=4\)

\(\Rightarrow\hept{\begin{cases}x^2=4\cdot16=64\\y^2=4\cdot49=196\end{cases}\Rightarrow\hept{\begin{cases}x=\pm8\\y=\pm14\end{cases}}}\)

Vì \(\frac{x}{4}=\frac{y}{7}\)nên x, y cùng dấu

\(\Rightarrow\hept{\begin{cases}x=-8\\y=-14\end{cases}}\)hoặc \(\hept{\begin{cases}x=8\\y=14\end{cases}}\)