`{ x + 1 }/{ x - 3 }` `-` `{ 1 - x }/{ x + 3 }` `+` `2x` `( 1 - x )`
`⇔` `{ ( x + 1 ) ( x + 3 ) - ( 1 - x ) ( x - 3 ) }/{ ( x - 3 ) ( x + 3 ) }` `+` `2x` `( 1 - x )`
`⇔` `{ 2x^2 + 9 + 2x ( 1 - x ) ( x - 3 ) ( x + 3 )/{ ( x - 3 ) ( x + 3 ) }`
`⇔` `{ - 2x^4 + 2x^3 + 20x^2 - 18x + 9 }/{ x^2 - 9 }`
$#Shawn$