Question

\(\dfrac{x+3}{9}=\dfrac{9}{x-3}\)

Answer 1

`(x-3)^2 = 81`

`<=>` \(\left[{}\begin{matrix}x-3=9\\x-3=-9\end{matrix}\right.\)

`<=>` \(\left[{}\begin{matrix}x=12\\x=-6\end{matrix}\right.\)

Answer 2

`(x+3)/9 = 9/(x-3)`

`(x-3)(x+3) = 9^2`

`x^2 -3^2 = 81`

`x^2 = 81-3^2 =81-9 `

`x^2 = 72`

\(\Rightarrow\left[{}\begin{matrix}x=\sqrt{72}=6\sqrt{2}\\x=-\sqrt{72}=-6\sqrt{2}\end{matrix}\right.\)

Vậy `x = +- 6sqrt{2}`