Which theorem establishes a relationship between the sides of a triangle in a circle?

Thales' Theorem

Thales' Theorem is often associated with a fascinating story from ancient Greece. Thales of Miletus, considered one of the seven sages, is said to have used this theorem to calculate the height of the Egyptian pyramids by measuring the length of their shadow and that of a vertically placed stick. This feat is not just a demonstration of human ingenuity, but also a testament to the practical application of mathematics in antiquity. The accuracy of his measurements, made without modern tools, remains a subject of admiration and study for mathematicians and historians. Furthermore, this ingenious method illustrates how mathematical concepts, although sometimes perceived as abstract, have concrete and powerful applications, capable of solving complex practical problems from the earliest civilizations.