( 2x + 3 ) ( 3x + 8/2 - 7x) + 1 ) = ( x - 5 ) ( 3x + 8/( 2 - 7x) + 1 )

`( 2x + 3 ) (( 3x + 8 )/( 2 - 7x ) + 1 ) = ( x - 5 ) (( 3x + 8 )/( 2 - 7x ) + 1 )`

`<=> ( 2x + 3 ) (( 3x + 8 )/( 2 - 7x ) + 1 )  - ( x - 5 ) (( 3x + 8 )/( 2 - 7x ) + 1 ) = 0 `

`<=> (( 3x + 8 )/( 2 - 7x ) + 1 ) .  [ ( 2x + 3 ) - ( x - 5 ) ] = 0 `

`<=> (( 3x + 8 )/( 2 - 7x ) + 1 ) . ( 2x + 3 - x + 5 ) = 0 `

`<=> (( 3x + 8 + 2 - 7x )/( 2 - 7 x)) . ( x + 8 ) = 0 `

`<=> ((  10 - 4x )/( 2 - 7x )) .  ( x + 8 ) = 0 `

`=> ( 10 - 4x ) . ( x + 8 ) = 0 `

`<=>`\(\left[ \begin{array}{l}10-4x=0\\x+8=0\end{array} \right.\) 

`<=>`\(\left[ \begin{array}{l}x=\dfrac{5}{2}\\x=-8\end{array} \right.\) 

Vậy ` S = { 5/2 ; - 8 } `