From the history of maths
Nicole Oresme
Around 1350 he proved that 1 + 1/2 + 1/3 + 1/4 + … grows without limit, by grouping its terms into halves.
He also drew graphs of changing quantities, about three centuries before Descartes.
Medieval manuscript illumination, Public domain, via Wikimedia Commons
Where you’ll meet Oresme here
Calculus
They turn up beside problems and lessons on these topics.
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Archimedes
Using 96-sided polygons he trapped π between 3 10/71 and 3 1/7.
He asked for a sphere inside a cylinder on his tomb, to mark his proof that the sphere fills two-thirds of it.
Painted in 1620; an imagined likeness. Domenico Fetti, Public domain, via Wikimedia Commons