Behind the theorem lies a fascinating historical figure: Thales of Miletus, the first mathematician “by name” in the Greek tradition.
History — Thales of Miletus and the height of the pyramid
Thales of Miletus (around 624—546 BC) is regarded as the first mathematician “by name” in the Greek tradition: before him, geometrical knowledge was collective and anonymous. The legend — reported by Plutarch, by Diogenes Laertius and by others — tells that Thales managed to measure the height of the Great Pyramid of Cheops simply by planting a stick in the sand and waiting for the moment when its shadow was equal to its height: at that instant the pyramid’s shadow too was equal to its height. It is, in fact, an application of the theorem on similar triangles — a century ahead of the Greek systematisation of geometry (Boyer, A History of Mathematics, ch. 3).
Thales is also credited with the first “proved” results of plane geometry: that the diameter divides the circle into two equal parts, that the base angles of an isosceles triangle are congruent, that vertically opposite angles are equal. These are the elementary building blocks of our book — and, in a certain sense, of all Western mathematics (Netz, ch. 1).
Links
Topics: Euclidean geometry
Concepts: Intercept theorem · Isosceles triangle
People: Thales