Curvature
Curvature is defined as the inverse of the radius length for circles. A line is treated as a circle with infinite radius, i.e. 0 curvature.
The formula for curvature of an arbitrary function is
![\[\dfrac{\frac{d^2y}{dx^2}}{((\frac{dy}{dx})^2+1)^{3/2}}\]](http://latex.artofproblemsolving.com/1/5/8/158ffe3fe419145283fc338c3a0c3a402018c4b6.png)
if y=f(x). A positive value indicates that the circle is above the function; a negative value, the circle is below.
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