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Dandelin Spheres. Dandelion image by Capri23auto from Pixabay

Dandelin’s Delightful Spheres

An ingenious use of spheres sheds light on this conic section

Mathematicians have been slicing open cones since the 4th Century BC. Here, we study one of these famous cross sections — the ellipse. Along the way, we’ll discover a beautiful proof from Germinal Dandelin of the 19th Century.

The Ellipse — Two Seemingly Unrelated…




Maths is like finger-painting. Messy and beautiful.

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Adam Hrankowski, ADHD

Adam Hrankowski, ADHD

Canadian math guy, experimenting with fiction. Find my new scifi/fantasy serial here:

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