Math Memes

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Memes related to mathematics.

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Behold a Square (sh.itjust.works)

submitted 1 month ago by pastermil to c/[email protected]

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[–] [email protected] 5 points 1 month ago (1 children)

You have the section of the smaller circle wrapping around the back of a narrower section of the cone, a right angle and then a straight line running down the side of the cone, another right angle in the other direction, then the section of the larger circle, this time going around the front of the cone, another right angle, and then the straight line completing the shape.

But you are right, the circle sections are not geodesics on that manifold, so not 'straight' by the most reasonable extension of that word to non -euclidian geometries. They'd be more like lines of latitude in that they seem straight from the outside, but in the context of that manifold are curved.

[–] [email protected] 2 points 1 month ago (1 children)

A cylinder would allow all geodesics, but then it would still have two 90 degree angles and two 270 degree angles so still not a square. I think it would be a trapezoid/trapezium, and might be a parallelogram depending on what definition you use.

There might be some crazy custom shape that makes the angles on the more complete circle segment actually 90 degrees but I don't think there's a common easy-to-conceive shape that works.

[–] [email protected] 2 points 1 month ago

still have two 90 degree angles and two 270 degree angles

But you just said internal vs. external angles was a distraction that people shouldn't get hung up on.

To be clear, apart from that one bit, I agree with you completely. I don't even necessarily disagree with what you said back there per se. I just don't think it was useful to bring it up because even if it isn't explicitly in the definition of a square, it is an implicit assumption that when talking about the angles of a shape, you're always talking about all internal angles (or, equivalently, all external angles, just no mixing), so getting "hung up on" internal vs. external angles is not a bad thing.