Details

This form of the Pythagorean theorem was first stated and proved in the hyperbolic plane by Maria Teresa Calapso in [1]. The theorem was then independently rediscovered in [2] and [3] on the sphere (see also [4]).

References

[1] M. T. Familiari-Calapso, "Sur une classe de triangles et sur le théorème de Pythagore en géométrie hyperbolique", Comptes rendus de l'Académie des sciences Série A-B, 268, 1969 pp. A603–A604.

[2] W. Dickinson and M. Salmassi, "The Right Right Triangle on the Sphere," The College Mathematics Journal, 39(1), 2008 pp. 24–33.

[3] P. Maraner, "A Spherical Pythagorean Theorem," The Mathematical Intelligencer, 32(3), 2010 pp. 46–50. doi:10.1007/s00283-010-9152-9.

[4] V. Pambuccian, "Maria Teresa Calapso's Hyperbolic Pythagorean Theorem," The Mathematical Intelligencer, 32(4), 2010 p. 2. link.springer.com/article/10.1007%2 Fs00283-010-9169-0.