From the history of maths
Thales of Miletus
Often called the first Greek mathematician. The theorem that an angle in a semicircle is a right angle carries his name.
He is said to have measured a pyramid’s height from the length of its shadow.
A Roman-era bust. Sailko, CC BY-SA 3.0, via Wikimedia Commons (resized)
Where you’ll meet Thales of Miletus here
Geometry
They turn up beside problems and lessons on these topics.
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David Hilbert
In 1900 he set out 23 problems that shaped twentieth-century mathematics.
His imaginary hotel with infinitely many rooms, always able to fit one more guest, is a favourite way to feel how strange infinity is.
Unknown author, Public domain, via Wikimedia Commons