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If a sentence starts with a mathematical variable which normally is lower case, should that variable be capitalized? Or is it better to just avoid starting sentences with variables?

  1. x and y represent the width and height of the anticuboctahedron.
  2. X and y represent the width and height of the anticuboctahedron.
  3. The width and height of the anticuboctahedron are represented by x and y.
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    X and x can represent different variables. They mustn't be confused. – Edwin Ashworth Dec 5 '13 at 22:02
  • My answer as a mathematician: The variable names should never be capitalised, x and X can very well be different variables. And variables at the beginning of a sentence should usually be avoided in writing. I wanted to add that something else that should be avoided are consecutive formulas without words or at least punctuation between them, but then I could not come up with an example, it seems to be more of a problem in German than in English. – Carsten S Dec 5 '13 at 22:07
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    No, this is not a duplicate of that question. Here's the answer I was prevented from posting: "Note that x in a mathematical equation is not a word; it's not really even a letter. It's a symbol. As such, it's not subject to the normal rules of orthography. As Edwin Ashworth noted in a comment, x must not be confused with X, which could represent something else: X is a different symbol from x. If you need to start a sentence with x, do that. Don't capitalise it." – Andrew Leach Dec 5 '13 at 22:07
  • This has been asked many times before. I find it a bit hard to pick one question, though. Especially since most of those questions are closed as duplicates themselves. Perhaps some merging is in order. – RegDwigнt Dec 5 '13 at 22:08
  • @Andrew Be my guest and pick any of these instead: 1, 2, 3. – RegDwigнt Dec 5 '13 at 22:10