[Turneyboy]

There are simple practical reasons though. We don't do that to be fancy. There are simply not enough letters in the latin alphabet to not have common intersection in writing. We like to use the same letters for objects of the same type (like x,y for coordinates or i,j,k,l for indices) because that increases readability significantly. But it does mean that you run out quite quickly.

Adding another alphabet alleviates those issues somewhat but even with greek letters added in we still run into this issue somewhat commonly.

[mindcrime]

There are simply not enough letters in the latin alphabet to not have common intersection in writing.

Agreed. But yet... some of the approaches taken to deal with that can be wildly annoying. Actually, using the Greek letters is probably the best of the lot, since they are a completely different set of characters with known pronunciations.

OTOH, sometimes you'll see people use both upper-case and lower-case latin letters in the same problem, forcing you to read it in stilted language like "The derivative of Big X with respect to y, plus the integral of Little x ..." Aaarrgggh.[1]

And then you get the "stylized" letters, which are (mostly) just Latin letters, but have no obvious unique pronunciation or verbalization without going through contortions. I mean, what do you say for "𝔑" especially if there is also a "n" on the page? And who's even going to recognize these monstrosities unless you're already a mathematician: 𝔖, 𝔚, 𝖄? Aaarrggggghhh.

[1]: to be fair, you could have the same problem with mixed case of Greek letters, but I haven't seen that as a common problem. But maybe that's only because I'm not a mathematician. shrug

[eru]

Well, you could use variable names longer than a single letter?

[the-smug-one]

It's a trade-off between brevity and verbosity, some mathematics do that. Often longer variable names are in ALL-CAPS. Since ab = a*b, it's important to differentiate vars from multiplications.