In rectangulis triangulis, quadratum, quod a latere rectum angulum subtendente describitur, aequale est eis, quae a lateribus rectum angulum cintinentibus describuntur, quadratis.
Translation
In right triangles, the square described by the side opposite the right angle is equal to the squares described by the sides adjacent to the right angle.
Author
Euclides
Reference
Evclidis Elementorum libri XV: Accessit liber XVI. Liber I, p. 147
