Profile cover photo
Profile photo
David Richeson
982 followers -
Mathematician
Mathematician

982 followers
About
David's posts

Post has attachment
I made two more impossible cylinders over the weekend: a triangle/square cylinder and a heart/diamond cylinder—a spade/club cylinder is left as a homework exercise :-) I have printable pdf templates on my blog so you can make your own. https://divisbyzero.com/2016/10/02/two-more-impossible-cylinders/
Photo
Photo
10/3/16
2 Photos - View album

Post has attachment
The September issue of Math Horizons is starting to appear in people's mailboxes. So I thought I'd post my article "Sugihara's Impossible Cylinder" http://users.dickinson.edu/~richesod/RichesonImpossibleCylinder.pdf (pdf). You can download a template so you can make your own impossible cylinder http://www.maa.org/sites/default/files/pdf/horizons/RichesonImpossibleCylinder.pdf (pdf). Also, I made a video showing the effect (below).

Post has attachment
Now you can wow your friends. I've created a printable template so you can make your own Sugihara object out of paper. https://divisbyzero.com/2016/07/06/make-a-sugihara-circlesquare-optical-illusion-out-of-paper/
Photo

Post has attachment
New blog post: I analyze Sugihara's optical illusion http://bit.ly/29wh1xo.
Photo

Post has attachment
The proof is trivial! (Note: hit refresh.)

Post has attachment
New on my blog: I've created measuring tapes that you can use to find the diameter and cross-sectional area of a cylinder or the volume and surface area of a sphere. 

Post has shared content
The international survey of opinion on mathematical journal reform has 432 responses so far. Please join in if you are in the target group: reader, author, reviewer or editor for a mathematical sciences journal in the last 3 years.


https://docs.google.com/forms/d/1r4LBUJk1VF9e4Dl4aXgS4fW-O8HR9yz1cqmXdzz0CjM/edit

Post has attachment
New on my blog: zip-apart Möbius bands.

Post has shared content
What is it like to do maths?

About 99% of the time it's like this. 
Photo

Post has attachment
Crockett Johnson (author of Harold and the Purple Crayon) proved that the isosceles triangle show below has angles with a 3:3:1 ratio. (He used it as part of a construction of a regular heptagon using a marked straightedge.) However, he used trigonometry to prove it. My question: Is there purely geometric proof of the theorem? If you have a proof (or if you know that someone has already proved it geometrically), let me know.

More details on my blog: http://divisbyzero.com/2016/03/23/a-geometry-theorem-looking-for-a-geometric-proof/
Photo
Wait while more posts are being loaded