"radius" . "Hudson" . "circumference of ellipse circumference" . . "pi" . "Selmer" . "minor" . "perimeter of ellipse perimeter" . "elliptic integral" . "(c) 2000-2023, Gerard Michon" . "geometry" . . "eccentricity" . "formula" . "mathematical" . . "formulas" . "There's no simple exact formula for the perimeter of an ellipse. The exact formulas aren't simple, and here's how good the simple ones really are:" . "oval" . "Kepler" . "Euler" . "mathematics" . "Circumference/Perimeter of an Ellipse: Formula(s) - Numericana" . "Ramanujan" . "major" . "calculate" . "Cantrell" . "osculating parabola" . "ellipse length" . "relative error" . "formulae" .