60/x−10 − 60/x = 1/5

` 60/( x - 10 ) - 60/x = 1/5 ( đk : x \ne 10 ; x \ne 0 ) `

`<=> ( 300x )/( 5x ( x - 10 )) - ( 300 ( x - 10 ))/( 5x ( x - 10 )) = ( x ( x - 10 ))/( 5x ( x - 10 )) `

`=> 300x - 300 ( x - 10 ) = x ( x - 10 ) `

`<=> 300x - 300x + 3000 = x^2 - 10x `

`<=> 3000 = x^2 - 10x `

`<=> 3000 - x^2 + 10x = 0 `

`<=> - x^2 + 10x + 3000 = 0 `

`<=> x^2 - 10x - 3000 = 0 `

`<=> x^2 - 60x + 50x - 3000 = 0 `

`<=> ( x^2 - 60x ) + ( 50x - 3000 ) = 0 `

`<=> x ( x - 60 ) + 50 ( x - 60 ) = 0 `

`<=> ( x - 60 ) ( x + 50 ) = 0 `

`<=>`\(\left[ \begin{array}{l}x-60=0\\x+50=0\end{array} \right.\) 

`<=>`\(\left[ \begin{array}{l}x=60( tm )\\x=-50( tm )\end{array} \right.\) 

Vậy ` S = { 60 ; - 50 } `