Prove (A, \cdot) is an abelian group where: A = {a \in \mathbb{Q} \mid a \neq -1},\quad a \cdot b = a + b + ab
Prove A, is an abelian group
Prove (A, \cdot) is an abelian group where: A = {a \in \mathbb{Q} \mid a \neq -1},\quad a \cdot b = a + b + ab