Thales’ rectangle

Thales of Miletus, a philosopher flourishing around 600 BCE, is credited with early geometric proofs. One notable theorem states that any angle inscribed in a semicircle is a right angle (90°). While his original proofs are lost, a proposed method known as Thales' rectangle demonstrates this theorem using geometric principles consistent with his era. This involves constructing a quadrilateral within a circle, utilizing properties of radii and congruent triangles to establish that the inscribed angle measures 90°. Thales is also recognized for his contributions to understanding geometry and his philosophical ideas, particularly his belief that water was the fundamental element of all matter.12