\(\dfrac{9\times42}{14\times27}\\ =\dfrac{3\times3\times6\times7}{7\times2\times3\times3\times3}\\ =\dfrac{3\times3\times6\times7}{7\times6\times3\times3}\\ =1\)

\(\dfrac{x-1}{3}=\dfrac{27}{x-1}\\ \Rightarrow\left(x-1\right)^2=27\cdot3\\ \Rightarrow\left(x-1\right)^2=81\\ \Rightarrow\left(x-1\right)^2=\pm8^2\\ \Rightarrow\left[{}\begin{matrix}x-1=8\\x-1=-8\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=9\\x=-7\end{matrix}\right.\)

`->` Ua?^^ La s? Toi khong ngo b la 1 con nguoi nhu v

-`->` thì sửa r đúng mà cái j v hả=))

đúng đó em cứ chép vô nha

keke=))