2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/69243This article deals with the history of certain aspects of the Pell equation X$^2$ - D y$^2$ = 4. We briefly discuss explicit units, and then study the history of Legendre's equations ax$^2$ - b y$^2$ = 4 with ab=D.19 pages, 2 figuresNumber TheoryHistory and Overview11D09; 11R11text