If , then
Landen's Transformation
See also
Elliptic Integral of the First Kind, Gauss's TransformationExplore with Wolfram|Alpha
References
Abramowitz, M. and Stegun, I. A. (Eds.). "Ascending Landen Transformation" and "Landen's Transformation." §16.14 and 17.5 in Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables, 9th printing. New York: Dover, pp. 573-574 and 597-598, 1972.Referenced on Wolfram|Alpha
Landen's TransformationCite this as:
Weisstein, Eric W. "Landen's Transformation." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/LandensTransformation.html