\(\dfrac{27}{3}=\dfrac{243}{27}=\dfrac{81}{9}\)

\(\dfrac{9}{3}=\dfrac{81}{27}=\dfrac{243}{81}\)

Ta có đăng thức :

3.81 = 9 . 27

=> ta lập đc các TL thứ là :

\(\dfrac{3}{9}=\dfrac{27}{81};\dfrac{3}{27}=\dfrac{9}{81};\dfrac{81}{9}=\dfrac{27}{3};\dfrac{81}{27}=\dfrac{9}{3}\)

Vậy ...

Ta có đẳng thức :

9 .81 = 243 . 3

=> ta lập đc các TL thứ là :

\(\dfrac{9}{243}=\dfrac{3}{81};\dfrac{9}{3}=\dfrac{243}{81};\dfrac{81}{243}=\dfrac{3}{9};\dfrac{81}{3}=\dfrac{243}{9}\)

Vậy ....

\(3\cdot81=9\cdot27\)

\(243\cdot3=9\cdot81\)

a: \(\left(-3\right)\cdot\left(-24\right)=6\cdot12\)

\(\Leftrightarrow\dfrac{-3}{6}=\dfrac{12}{-24};\dfrac{-3}{12}=\dfrac{6}{-24};\dfrac{6}{-3}=\dfrac{-24}{12};\dfrac{12}{-3}=\dfrac{-24}{6}\)

b: \(12\cdot0.9=18\cdot0.6\)

\(\Leftrightarrow\dfrac{12}{18}=\dfrac{0.6}{0.9};\dfrac{12}{0.6}=\dfrac{18}{0.9};\dfrac{18}{12}=\dfrac{0.9}{0.6};\dfrac{0.6}{12}=\dfrac{0.9}{18}\)

Có thể và các tỉ số đó là:
\(\dfrac{3}{9}=\dfrac{81}{243}\) \(\dfrac{9}{27}=\dfrac{81}{243}\) \(\dfrac{3}{27}=\dfrac{9}{81}\)

\(\dfrac{3}{81}=\dfrac{9}{243}\) \(\dfrac{9}{81}=\dfrac{27}{243}\) \(\dfrac{3}{9}=\dfrac{27}{81}\)

\(\dfrac{9}{3}=\dfrac{243}{81}\) \(\dfrac{27}{9}=\dfrac{243}{81}\) \(\dfrac{9}{3}=\dfrac{81}{27}\)

\(\dfrac{243}{9}=\dfrac{81}{3}\) \(\dfrac{81}{9}=\dfrac{243}{27}\) \(\dfrac{81}{9}=\dfrac{27}{3}\)

Có thể và các tỉ lệ thức là :

\(\dfrac{3}{9}=\dfrac{81}{243}\);\(\dfrac{3}{81}=\dfrac{9}{243}\);\(\dfrac{9}{3}=\dfrac{243}{81}\);

\(\dfrac{243}{9}=\dfrac{81}{3}\)

\(\dfrac{9}{27}=\dfrac{81}{243}\);\(\dfrac{9}{81}=\dfrac{27}{243}\);\(\dfrac{27}{9}=\dfrac{243}{81}\);

\(\dfrac{81}{9}=\dfrac{243}{27}\)

\(\dfrac{3}{27}=\dfrac{9}{81}\); \(\dfrac{3}{9}=\dfrac{27}{81}\); \(\dfrac{9}{3}=\dfrac{81}{27}\); \(\dfrac{81}{9}=\dfrac{27}{3}\)

theo bài ra ta có các đẳng thức sau:

\(3.243=9.81\\ 3.81=9.27\\ 9.243=27.81\)

từ mỗi đẳng thức trên ta suy ra các tỉ lệ thức :
\(\dfrac{3}{9}=\dfrac{81}{243};\dfrac{3}{81}=\dfrac{9}{243};\dfrac{243}{9}=\dfrac{81}{3};\dfrac{243}{81}=\dfrac{9}{3}\)

\(\dfrac{3}{9}=\dfrac{27}{81};\dfrac{3}{27}=\dfrac{9}{81};\dfrac{81}{9}=\dfrac{27}{3};\dfrac{81}{27}=\dfrac{9}{3}\\ \dfrac{9}{27}=\dfrac{81}{243};\dfrac{9}{81}=\dfrac{27}{243};\dfrac{243}{27}=\dfrac{81}{9};\dfrac{243}{81}=\dfrac{27}{9}\)

chúc bn học tốt

Bài 2: 

a) \(\frac{x}{-27}=\frac{-3}{x}\Leftrightarrow-\frac{x}{27}=-\frac{3}{x}\Leftrightarrow-x.x=\left(-27\right).\left(-3\right)\Leftrightarrow-x^2=-81\Leftrightarrow\orbr{\begin{cases}x=9\\x=-9\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=9\\x=-9\end{cases}}\)

b) \(\frac{-9}{x}=\frac{-x}{\frac{4}{49}}\Leftrightarrow-\frac{9}{x}=-\frac{49x}{4}\Leftrightarrow-9.4=-x.49x\Leftrightarrow-36=-49x^2\Leftrightarrow\orbr{\begin{cases}x=\frac{6}{7}\\x=-\frac{6}{7}\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=\frac{6}{7}\\x=-\frac{6}{7}\end{cases}}\)

Ta có: 9 x 27 = 3 x 81 

Các tỉ lệ thức lâp được là: 3/9 = 27/81 ; 3/27 = 9/81 ; 9/3 = 81/27 ; 27/3 = 81/9