For example on this wikipedia page:

一方、右辺第二項は R → ∞ のとき 0 に収束するので、...

In English it would be something like "as R goes to infinity". How would you usually read this in Japanese?

  • 4
    From this answer: 数式記号の読み方・表し方.
    – blutorange
    Commented Mar 5, 2016 at 16:40
  • 3
    It's perfectly okay to ask questions of this nature on Japanese.SE :-)
    – user1478
    Commented Mar 5, 2016 at 19:08
  • 1
    We need some word to express this.
    – user4092
    Commented Mar 6, 2016 at 13:05
  • 4
    俗には "R を無限大に飛ばすとき" という言い方もありますね.
    – Yosh
    Commented Mar 7, 2016 at 5:18
  • I participate in math stack exchange, english and japanese wiki.I can say mathematical expression are almost same all over the world. Commented Mar 9, 2016 at 11:35

2 Answers 2


R → ∞

is usually read

R を限りなく大きくする[と・とき]
R が限りなく大きくなる[と・とき]

I don't think that 「R → ∞ のとき」 is supposed to have a fixed natural pronunciation. You can ignore the の and read it as above, or you could probably read it as

[R]{アール} [→]{トゥ} [∞]{インフィニティ} のとき
[R]{アール} [→]{ツー} [∞]{インフィニティ} のとき

  • 3
    +1 for a mathematician on this site. :) It's interesting that the wikipedia page on limits 極限 does not explain how to read the notation while the English version does. Hmmm. Though you could perhaps infer it from the context.
    – A.Ellett
    Commented Mar 5, 2016 at 16:30

In Japanese,

  • R is pronounced aaru (アール)
  • → is pronounced yajirusi (矢印【やじるし】)
  • ∞ is pronounced mugendai (無限大【むげんだい】)

I think "n→∞" is often pronounced as follows in the differential and integral.

  • エヌ矢印無限大 enu yajirusi mugendai
  • エヌ無限大 enu mugendai

where enu (エヌ) means the letter N.

Therefore I guess that "R→∞" is pronounced in the same way.

Although, because it is terminology, I guess it does not have a clear colloquial pronunciation.

It seems that there are some people who call it aaru twu infinithi (R to infinity) in Japanese English.

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