\(a.\) \(\frac{x}{3.15}\) \(=\) \(\frac{0.15}{7.2}\) 

<=> \(x=\) \(\frac{0.15\cdot3.15}{7.2}\) 

<=>\(x=0.065625\)

\(b.\) \(\frac{-2.6}{x-11}=\frac{-12}{42}\) 

<=>\(x-11=\frac{-2.6\cdot-12}{42}\)

<=>\(x-11=0.742857142\)

<=>\(x=11.74285714\)

\(3\frac{4}{5}:2x=0,25:2\frac{2}{3}\)

\(\Leftrightarrow\frac{19}{5}:2x=0,25:\frac{8}{3}\)

\(\Leftrightarrow\frac{19}{5}:2x=0,25\cdot\frac{3}{8}\)

\(\Leftrightarrow\frac{19}{5}:2x=\frac{3}{32}\)

\(\Leftrightarrow2x=\frac{19}{5}:\frac{3}{32}=\frac{19}{5}\cdot\frac{32}{3}=\frac{608}{15}\)

\(\Leftrightarrow x=\frac{608}{15}:2=\frac{608}{30}=\frac{304}{15}\)

\(\frac{x}{3,15}=\frac{0,15}{7,2}\)

\(\Rightarrow7,2x=0,15\cdot3,15=0,4725\)

\(\Rightarrow x=0,4725:7,2=0,065625\)

\(\frac{x}{3,15}=\frac{0,15}{7,2}\)

=> x.7,2 = 3,15.0,15

=> x.7,2 = 0,4725

=>       x = 0,4725 : 7,2

=>       x = 0,065625

    Vậy x = 0,065625 

\(\frac{x}{3,15}=\frac{0,15}{7,2}\)

\(\Rightarrow x.7,2=3,15.0,15\)

\(x.7,2=0,4725\)

\(x.\frac{72}{10}=\frac{4725}{10000}\)

\(x=\frac{4725}{10000}:\frac{72}{10}\)

\(x=\frac{47250}{720000}=\)tự rút gọn 

Trả lời nè bạn ưi !!!

x=(3,15.0,15): 7,2

x=\(\frac{21}{320}\)

Chúc thành công.

Có : \(\frac{x}{3,15}=\frac{0,15}{7,2}\Rightarrow x=\frac{0,15.3,15}{7,2}=\frac{21}{320}\)

\(\frac{x}{3,15}=\frac{0,15}{7,2}\)

\(\Rightarrow x.7,2=3,15.0,15\)

\(\Rightarrow x.7,2=\frac{189}{400}\)

\(\Rightarrow x=\frac{189}{400}:7,2\)

\(\Rightarrow x=\frac{21}{320}\)

Vậy \(x=\frac{21}{320}.\)

Chúc bạn học tốt!

\(2x\left(x-\frac{2}{3}\right)=0\)

\(\Rightarrow\orbr{\begin{cases}2x=0\\x-\frac{2}{3}=0\end{cases}\Rightarrow\orbr{\begin{cases}x=0\\x=\frac{2}{3}\end{cases}}}\)

\(\frac{37-x}{x+13}=\frac{3}{7}\)

\(\left(37-x\right).7=\left(x+13\right).3\)

\(259-x7=x3+39\)

\(x7-x3=39-259\)

\(x4=-220\Leftrightarrow x=-55\)

a)\(\frac{x}{3,15}=\frac{0,15}{7,2}\)

\(\Rightarrow7,2x=3,15.0,15\)

\(7,2x=0,4725\)

       x = 0,4725:7,2

       x=0,065625

b) \(2x\left(x-\frac{2}{3}\right)=0\)

\(\Rightarrow\orbr{\begin{cases}2x=0\\x-\frac{2}{3}=0\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=0:2=0\\x=0+\frac{2}{3}=\frac{2}{3}\end{cases}}\)

Vậy........................................

\(c)\frac{37-x}{x+13}=\frac{3}{7}\)

\(\Rightarrow\left(37-x\right)7=3\left(x+13\right)\)

259-7x=3x+39

-7x-3x=39-259

-10x=-220

     x=-220:(-10)

     x=22

a) \(\frac{x}{3,15}=\frac{0,15}{7,2}\)

suy ra 7,2. x= 0,15.3,15

x= 0,15.3,15 : 7,2

x= \(\frac{21}{320}\)

b) suy ra 2x=0 hoặc x-2/3=0

suy ra x=0 hoặc x=2/3

Vậy x thuộc {0; 2/3}

c) \(\frac{37-x}{x+13}=\frac{3}{7}\)

suy ra 7.(37-x) = 3.(x+13)

259-7x=3x+39

x+3x = 259-39

4x=220

x=55

Vậy x=55

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

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

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

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

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

\(-\frac{2,6}{x}=-\frac{12}{42}\)

\(-2,6\cdot42=-12\cdot x\)

\(\frac{109,2}{12}=x\Rightarrow x=9,1\)