# Bezier curvature

I'm trying to understand quadratic Bezier curves but I cannot get pass one thing. Please, what is a "curvature" and how can I calculate it?

I'm asking because I found for instance:
http://blog.avangardo.com/2010/10/acceleration-on-curve-path/
http://en.wikipedia.org/wiki/Curvature

but I also saw:
Curvature = (P1x - P2x)(P3y - P2y) - (P3x - P2x)(P1y - P2y)
where P1, P2, P3 are points defining the curve.

There problem is, I don't see how one could arrive to such formula - could someone explain it to me?

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