1. The problem statement, all variables and given/known data This is an exercise from the book 'Mathematical Proofs: A transition to advanced mathematics'. Prove that if r is in ℝ and 0<r<1, then 1/r(1-r)≥4 3. The attempt at a solution My guess is that it would be best to use a proof by contrapositive. So I start by assuming that 1/r(1-r)<4 then rearrange the equation to find that r≤0 and r≥1. If that approach is right then my poor algebra is the reason I can't complete the proof. Is this the right approach?