John Rock

Continuity

I've been learning how to build Desmos activities for real analysis. This one helps build some intuition about the definition of continuity, and in turn it really helps motivate the search for a good threshold delta. www.desmos.com/calculator/e...

13.02.2026 05:25 — 👍 11    🔁 4    💬 0    📌 0

I made a mistake! A whole bunch of them, actually. Check them out in the errata for my textbook "Arbitrarily Close: An Introduction to Real Analysis": www.cpp.edu/faculty/jaro.... An updated PDF of the textbook with slightly fewer mistakes free to download.

30.01.2026 16:41 — 👍 1    🔁 0    💬 0    📌 0

Cover of the textbook Arbitrarily Close: An Introduction to Real Analysis.

Arbitrarily Close: An Introduction to Real Analysis has been published by 619 Wreath! Free PDF, Desmos, and GeoGebra available on my faculty webpage (at least for the time being): www.cpp.edu/faculty/jaro...

Hardcover and paperback copies are available from 619 Wreath: www.619wreath.com/acl.html

25.10.2025 19:45 — 👍 10    🔁 4    💬 0    📌 0

100-45=55. Then add 12 to get 67. I wonder what other people will try?

15.09.2025 21:49 — 👍 2    🔁 0    💬 0    📌 0

I want to be romantic about baseball, but it broke my heart tonight instead

16.07.2025 04:04 — 👍 2    🔁 1    💬 0    📌 0

Hey remember when the one of the most prominent Democrats in Minnesota and her husband were assassinated

22.06.2025 03:38 — 👍 579    🔁 125    💬 8    📌 5

If you do the alternating sum of the digits of a whole number, you can tell if that number is divisible by 11. Here's how and why it works:

28.05.2025 01:28 — 👍 31    🔁 5    💬 0    📌 2

Walz: If you say you love freedom but you don't believe freedom is for everybody, then the thing you love is not freedom, it is privilege.

24.04.2025 00:22 — 👍 79231    🔁 20278    💬 839    📌 1262

A tweet by Sarah Longwell (@SarahLongwell25 ) reads: "He’s threatening media companies who are critical of him. He’s talking about sending Americans to foreign prisons. He’s signing executive orders to investigate former staff members who spoke out against him. Don’t you see what’s happening here?"

I see it. I have lived it. 83 years ago, the U.S. government turned upon a group of its own citizens and residents and sent them to internment camps without due process. I was there among them. American fascism is back. It is here. It is now.

15.04.2025 20:30 — 👍 45363    🔁 14458    💬 958    📌 482