Why was this visual proof missed for 400 years? (Fermat's two square theorem)

MathType on X: Lagrange's four-square theorem asserts that any positive whole number can be written as the sum of four squares of integers. Leave an example in the comments! #MathType #NumberTheory #math #

PDF) Lagrange's Four-Square Theorem

Jacobi's four-square theorem - Wikipedia

PDF) A Simple Proof of Jacobi's Four-Square Theorem

Lagrange's four-square theorem - Wikiwand

number theory - The Four Square Theorem and Integral Apollonian Circle Packings, is there any connection? - Mathematics Stack Exchange

Waring's Problem -- from Wolfram MathWorld

Lagrange's Four-Square Theorem Seen Using Polygons and Lines - Wolfram Demonstrations Project

An Independent Quaternion Proof of Jacobi's Four Square Theorem: Zhang, Yuxuan: 9781719171571: : Books

Lagrange's Four-Square Theorem Seen Using Polygons and Lines