I don't think the proof is correct: you use the mean value theorem, but that theorem only applies to differentiable functions. At that point you don't know yet that F is differentiable. Modern proofs do not rely on geometry. This is a faulty approach. RoseParks Where does geometry come into this? Besides, proofs are either correct or incorrect. Whilst we should strive for elegance, an inelegant proof is still a proof. GWO |
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