Which one is correct? $(n/2)$nd or $(n/2)$th?

Question

I am reading a textbook in which I find a writing problem:

Squaring them produces the $(n/2)$nd roots of unity.

My question:

@Doop: that's probably true. I suspect you might say something like "$n$-halfth", though, which in symbols probably looks like $(n/2)^\text{th}$. — Dejan Govc, Apr 06 '14 at 08:02
Maybe English.SE is a reasonable candidate for this question? It seems similar
to this question (k+1)th or (k+1)st? — Martin Sleziak, Apr 06 '14 at 08:25
1.I am not sure where to ask, but I know I want answer from mathmatician or math students. 2.The people in english.SE says " Because this is localized to mathematics, it might be worthwhile trying it on the math.SE site" — Jill Clover, Apr 06 '14 at 08:27
You are saying: Because this is localized to mathematics, it might be worthwhile trying it on the math.SE site. Where are you quoting from? Can you provide a link? (I do not see such question in your English.SE profile.) — Martin Sleziak, Apr 06 '14 at 11:50
I should mention, that the question about (k+1)th vs. (k+1)st has also been asked here: http://math.stackexchange.com/questions/55200/k1th-k1st-k-th1-or-k1 (I found this only after I had posted the above comment.) — Martin Sleziak, Apr 06 '14 at 11:51
Ok, now I see that what you quoted above @J.A.F is a comment which was given on English.SE for the question about (k+1)th vs. (k+1)st. (The way you phrased your comment, I thought that you are talking about this question.) — Martin Sleziak, Apr 06 '14 at 12:09
@MartinSleziak Thanks!This is what I am looking for http://math.stackexchange.com/questions/55200/k1th-k1st-k-th1-or-k1 — Jill Clover, Apr 06 '14 at 12:30
I have voted to reopen. If there is need to discuss whether this question is on-topic or off-topic, we should discuss such things on meta, there already exists a thread about this question. — Martin Sleziak, Apr 06 '14 at 13:57

score 1 · Answer 1 · answered Apr 06 '14 at 08:36

It is best to use the regular -th suffix to form ordinal adjectives if the denotation of the cardinal number includes any non-numeric symbols. This is logical, because the "th" belongs to the whole number that is denoted, not just to the last digit that happens to occur in the expression. Also use -th for an explicit number not ending with 1, 2, or 3, and when it ends with with 11, 12, or 13. Incidentally, I would read your example as "the half-enth roots of unity".

Which one is correct? $(n/2)$nd or $(n/2)$th?

1 Answers1