Changing of radiuses of curvature of a curve generally can match with that of either of conic sections when the change is continuous. With this feature arcs of functional curves are approximated by conic sections. It leads a method of numerical solution of functions being difficult otherwise to be solved. Because of the second degree, equations of conic section can be easily solved even if reversely. As a practical example reduction of the tristimulus value Y to the Munsell value V about colors, an equation of the fifth degree, is treated by the approximation with an equation of hyperbola.
