Dave Richeson (@divbyzero) / X

Dave Richeson

21.5K posts

Dave Richeson

@divbyzero

Mathematician. Curley Chair in Liberal Arts at Dickinson College. Author of Tales of Impossibility and Euler's Gem. Now: divbyzero.bsky.social

Carlisle, PA

Joined August 2008

Pinned
Dave Richeson
@divbyzero
Nov 17, 2024
I don't know my plan for Twitter/X. It is hard to give up after all the great people I've met and conversations I had in 13+ years, but the math community has moved to Bluesky. I will use divbyzero.bsky.social as my go-to site for posting math content now. Join us there!
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Dave Richeson
@divbyzero
Aug 20, 2022
My friend got these pudding cups. (As in, “the proof is in the pudding.”)
Dave Richeson
@divbyzero
May 4, 2023
Cool proof and cool example of using CSS to create mathematical animations on web pages! Here's the page with the math x.st/visual-sum-of-… and here's the page describing the CSS x.st/spinning-diagr….
GIF
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Dave Richeson
@divbyzero
Jun 17, 2023
Nice puzzle posted by @icecolbeveridge on Mastodon (that he said came from Reddit): Toggle one pixel to make this correct. No spoilers for those who don't see it!
1.2M
Dave Richeson
@divbyzero
Sep 1, 2022
A pile of granular material has a maximum slope on its side. This is known as the "angle of repose." I measured the angle of repose of ordinary table salt to be about 33.5°. By pouring salt on raised shapes you can obtain interesting geometric patterns. 1/5
Dave Richeson
@divbyzero
Jul 30, 2023
All of the plenary talks were amazing at Bridges this year! @mathgrrl gave the last one, and during the talk she gave everyone a 3D printed copy of this knot, which has the surprising property there does not exist a plane that is tangent to the knot in three places. So it rolls!
00:00
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Dave Richeson
@divbyzero
Sep 3, 2022
My son, a first-year college students, just called me to say he is going to LaTeX his math notes. ("How do you do piecewise functions?") ♥️♥️ So I had to send him my LaTeX cheat sheet users.dickinson.edu/~richesod/late… and the Intro to LaTeX video I made youtube.com/watch?v=NXW4cb…
Dave Richeson
@divbyzero
Dec 9, 2022
Topological magic trick: Draw a rectangular border around a piece of paper. Tell the audience member that they will be drawing a simple closed curve on the paper—the more complicated they make it, the better. It can (and should) go in and out of the border rectangle 1/11
Dave Richeson
@divbyzero
Oct 19, 2018
I made this fun graphic: I ♥ Math. It is now in the latest issue of the British magazine @chalkdustmag (the version appearing there has the British "maths"). chalkdustmagazine.com/regulars/i-hea…
Dave Richeson
@divbyzero
Dec 19, 2021
When I was a kid I used to make this sketch: connect (1,0) to (0,10), (2,0) to (0,9), etc. I thought it was cool that these straight lines had a curved boundary. Now I know that this curve is called the *envelope* of the family of lines. What is this curve? 1/7
Dave Richeson
@divbyzero
Nov 18, 2019
LaTeX realhats package—\hat{a} put real hats (dunce cap, Santa hat, top hat, cowboy hat, etc.) on symbols instead of â. ctan.org/pkg/realhats
Dave Richeson
@divbyzero
Dec 19, 2023
Why, yes, I did just make this math joke/dad joke for my daughter who is taking calculus right now just to see her eye roll! "Sky's the limit!"
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Dave Richeson
@divbyzero
Aug 22, 2022
A topological magic trick. (Mathematical explanation in the next tweet.)
00:00
Dave Richeson
@divbyzero
Jul 17, 2023
Draw a line from (0,10) to (1,0), from (0,9) to (2,0), and so on. This set of lines has a curved envelope. That curve is a parabola (with equation (x+y−11)²−4xy=0). Here's a still image. Animations in the following tweets. 1/3
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