`(x+6)(720/x -4)=720` Giải pt

`(x + 6)(720/x - 4) = 720`

`<=> 720 - 4x + 4320/x - 24 = 720`

`<=> 720x -  4x^2 + 4320 - 24x = 720x`

`<=> 696x - 4x^2 + 4320 = 720x`

`<=> 696x - 4x^2 + 4320 - 720x = 0`

`<=> -24x - 4x^2 + 4320 = 0`

`<=> -4( 6x + x^2 -1080) = 0`

`<=> 6x + x^2 - 1080 = 0 : (-4)`

`<=> 36x - 30x + x^2 - 1080 = 0`

`<=> x(x + 36) -30(x + 36) = 0`

`<=> (x + 36(x - 30) = 0`

`<=>` $\left[\begin{matrix} x + 36 = 0\\ x - 30 = 0\end{matrix}\right.$
`<=>` $\left[\begin{matrix} x = -36\\ x = 30\end{matrix}\right.$

Vậy `S = {-36; 30}`