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[-] Knock_Knock_Lemmy_In@lemmy.world 2 points 20 hours ago

Define straight in a precise, mathematical way.

[-] ltxrtquq@lemmy.ml 8 points 19 hours ago

The tangent of all points along the line equal that line

[-] wholookshere@lemmy.blahaj.zone 1 points 14 hours ago* (last edited 14 hours ago)

Only true in Cartesian coordinates.

A straight line in polar coordinates with the same tangent would be a circle.

EDIT: it is still a “straight” line. But then the result of a square on a surface is not the same shape any more.

[-] ltxrtquq@lemmy.ml 3 points 13 hours ago

A straight line in polar coordinates with the same tangent would be a circle.

I'm not sure that's true. In non-euclidean geometry it might be, but aren't polar coordinates just an alternative way of expressing cartesian?

Looking at a libre textbook, it seems to be showing that a tangent line in polar coordinates is still a straight line, not a circle.

[-] wholookshere@lemmy.blahaj.zone 1 points 5 hours ago

I’m saying that the tangent of a straight line in Cartesian coordinates, projected into polar, does not have constant tangent. A line with a constant tangent in polar, would look like a circle in Cartesian.

[-] ltxrtquq@lemmy.ml 2 points 4 hours ago

Polar Functions and dydx

We are interested in the lines tangent a given graph, regardless of whether that graph is produced by rectangular, parametric, or polar equations. In each of these contexts, the slope of the tangent line is dydx. Given r=f(θ), we are generally not concerned with r′=f′(θ); that describes how fast r changes with respect to θ. Instead, we will use x=f(θ)cosθ, y=f(θ)sinθ to compute dydx.

From the link above. I really don't understand why you seem to think a tangent line in polar coordinates would be a circle.

this post was submitted on 21 Sep 2024
1161 points (97.2% liked)

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