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# Category Archives: geometry

## Orthogonal polygons

It’s time to say more about PWW #21, in which I exhibited things like this: Quite a few commenters figured out what was going on, and mentioned several nice (equivalent) ways to think about it. Primarily, the idea is to … Continue reading

## Post without words #21

Posted in combinatorics, geometry, posts without words
Tagged enumeration, orthogonal, polygons
17 Comments

## Paper torus with Villarceau circles

I made another thing! This is a torus, made from 24 crescent-shaped pieces of paper with slots cut into them so they interlock with each other. I followed these instructions on cutoutfoldup.com. There is also a template with some ideas … Continue reading

## Computing sums of primitive roots

Remember this picture? It, and other pictures like it, express the fact that for a given , if we take the primitive roots for each of the divisors of , together they make up exactly the set of all th … Continue reading

## Sums of primitive roots

In my previous post, we saw that adding up all the complex th roots of unity always yields zero (unless , in which case the sum is ). Intuitively, this is because the roots are symmetrically distributed around the unit … Continue reading

## Sums and symmetry

Let’s continue our exploration of roots of unity. Recall that for any positive integer , there are complex numbers, evenly spaced around the unit circle, whose th power is equal to . These are called the th roots of unity. … Continue reading

## Curvahedra

Everyone should go check out this Kickstarter project for CURVAHEDRA, a sort of construction kit that lets you build beautiful stuff like this: So cool! You can read more about the math behind them here. These are designed by Edmund … Continue reading

Posted in geometry, links
Tagged construction, Curvahedra, Kickstarter, polyhedra