Fill-in-the-blank proofs for Section 4.3

1. Claim: The function f : (0, ∞) → (5, ∞) with rule f(x) = 3x + 5 is onto.
   Proof. Click here.
   
2. Claim: The function f : N → Q with rule f(x) = 2/(x + 1) is one-to-one.
   Proof. Click here.
   
3. Claim: If the function f : Q → Q is onto, then the function g : Q→ Q with rule g(x) = f(2x) is onto.
   Proof. Click here.
   
4. Claim: If the function f : Z → Z is one-to-one, then the function h : Z → Z with rule h(x) = f(2x) is one-to-one.
   Proof. Click here.