Physically/conceptually, I understand why the unit normal vector will always point toward the side of concavity on a curve. It's because the unit normal's direction is the derivative of the unit tangent, and the unit tangent's change in direction is always toward the concave side.(adsbygoogle = window.adsbygoogle || []).push({});

But how is this represented mathematically? I tried to prove it, but I'm stuck. I've looked, but I couldn't find any proofs about this. Does anyone know?

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# Unit Normal always pointing toward concave side

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