hey did you know the roots of a cubic polynomial can be visualized using an equilateral triangle?

🔵 vertices are roots
🔴 the incenter is the inflection point
🟢 the incircle boundaries are the local minima/maxima

@acegikmo That looks really cool.

Would you mind telling me which library or program you used for the animation?

I recently did one using 3b1b's manim, which was a pleasant but a bit underdocumented experience.

@teraku Unity (the game engine) with my own library (Shapes) for vector graphics and a custom recording tool!
@acegikmo I really enjoy all the geometric images and animations you share. Thank you for posting them.
@acegikmo Does that mean that if you now where 2 of those points are you can easily calculate the rest of them from the properties of a triangle?

@acegikmo Wow, that is great!

That makes it much more clear why solutions to cubic polynomials involve trigonometric functions!

GraphicsGems/Roots3And4.c at master · erich666/GraphicsGems

Code for the "Graphics Gems" book series. Contribute to erich666/GraphicsGems development by creating an account on GitHub.

GitHub
@acegikmo It’s so mesmerising  
@acegikmo this is the kind of nerdy shit I like. Moar.
@acegikmo What in the mathematical, how does that...it's because of complex numbers, isn't it?
@acegikmo I understood some of these words.😅

@acegikmo

*let me in meme*
MAKE THE TRIANGLE SPIN!! 😱

(I mean: make the local max go below the x-axis; the blue dots will still be on the graph; do they relate to the complex roots??)

Also, make the max/min pass through eachother and swap places !!?? ⭕ 💥

@acegikmo every time you post I learn something that I would have never learned in a million years. Thanks for sharing so many interesting visuals!
@acegikmo Truly mesmerising! 🤩

@acegikmo @quantum A generalization to complex cubic polynomials is Marden's theorem.

There is an ellipse, called Steiner's ellipse, inscribes the triangle formed by the roots of \( f(z)=0 \) at the middle points of the edges, and its two focuses are the roots of 𝑓'(𝑧)=0.

See Albert Chern's Twitter post
https://twitter.com/theAlbertChern/status/1395468792788967428?s=20

And this blog article by @johncarlosbaez :

https://johncarlosbaez.wordpress.com/2021/05/24/electrostatics-and-the-gauss-lucas-theorem/

Albert Chern on Twitter

“Guess what? In 2D electrostatics, the saddles of the electric potential from 3 equal point charges are the foci of the biggest ellipse contained in the triangle of the charges.”

Twitter
@acegikmo 👏 👏 I liked this diagram and was chipping away at improving my plotting setup, so I made an interactive version of it. https://rreusser.github.io/cubic-roots/
Cubic Roots ↔︎ Equilateral Triangle

An interactive reproduction of a diagram by Freya Holmér