2 ( x + 2 b ) = a ( a b − x ) →
→ 2 · x + 4 · b = a 2 b − a · x → ( 2 + a ) · x = a 2 b − 4 · b → ( 2 + a ) · x = ( a 2 − 4 ) · b
A ( a ) = 2 + a e B ( a , b ) = ( a 2 − 4 ) · b = ( a + 2 ) ( a − 2 ) · b
Posto A ( a ) = 0 → a = − 2 . Posto B ( a , b ) = 0 → b = 0 ∨ a = 2 ∨ a = − 2