Which indefinite article should i use before "one", eg, "a one dimensional line" or "an one dimensional line"?

a

Here you go :)

Oops, sorry rob, I was a little too late

You should use “a” because even though “one” starts with a vowel it makes the consonant sound of “W.”

An ostrich, a unicorn, a whoop-de-do, a whippersnapper. English is very odd for the non-native speaker, and for some native speakers, also.

And “one dimensional” should be hyphenated because it precedes a noun.

@gail, I agree. And on tangent, I’m increasingly of the opinion that I might start using mouses as a plural as that’s the more consistent form in general, especially if one wishes to consider houses as establishing precedent.

Here is a phunnee essay on hyphens

And another on The Semicolon

rob: I used to spend a lot of time with ESL students and still refer to things as mouses and fishies and sheepies. (the ies was my method of not sounding like a fool in other situations. Most just assumed I had a little sibling.