1. The problem statement, all variables and given/known data f:]1,+∞[→]2,+∞[ x→ 2x/(x-1) 2. Relevant equations Prove that f is injective and serjective. 3. The attempt at a solution I already proved that it's injective by stating the injectivity law: for every (a,b)ε]1,+∞[: f(a)=f(b) implies a=b so: 2a/(a-1)=2b/(b-1) entails: 2ab-2b=2ab-2a entails -2b=-2a entails a=b Can anyone please tell me how to prove that its serjective?