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CURVATURE

We have defined the curvature as the slope of the slope, d(dy/dx)/dx = d²y/dx², in order to give an "obvious" meaning to the second derivative. Although this definition is simple, intuitive and useful, it is not the conventional mathematical definition   d/ds,   where is the tangential angle and s is the arc length.

(So shoot me. I still like mine better.   ;-)       Thanks to Mitchell Timin for pointing this out.