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

Lagrange's four-square theorem - Wikipedia

Solved {(x,y,z,w).M: x,y,z, w € Z} Theorem 8.35 (Lagrange's

Lagrange's four-square theorem, polynomials, diophantine equations, prime numbers

Solved QUADRA range's Four-Square Theorem) If n is a natural

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

PDF) Quarternions and the Four Square Theorem

Lagrange's Four Square Theorem

Solved Lagrange's four square theorem says every natural

Pythagorean Theorem

Chapter 3 Greek Number Theory The Role of Number Theory Polygonal, Prime and Perfect Numbers The Euclidean Algorithm Pell's Equation The Chord and Tangent. - ppt download