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I just had this terrifying conversation:

> What is "triangle" in Japanese?
>
> me: 三角 right?
>
> Then what's 三角形?
>
> me: Uhh... triangle?

I've confirmed both of these translate to "triangle". Apparently they refer to
different _aspects_ of the triangle in Japan? Is 三角 a symbol and 三角形 a
geometrical form?
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2012-08-07T06:37:19.010
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word-choice mathematics
What's the difference between 三角 and 三角形?
It might be something as simple as:

> 三角 (something that is "triangular" where the focus is having attributes
> similar to that of triangles ie: three sides, three corners)
>
> 三角形 (a polygon that IS a triangle)

For example: 「三角屋根」 is a way to describe a roof that is "triangular" in
comparison to other roofs of different shapes. It has attributes similar to
those of "triangles".
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2012-08-07T07:09:12.153
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2012-08-08T05:16:29.743
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ya know sometimes what natives say can be misleading and not actually
reflective of their intuitions. i think the difference is just as Chris says,
"triangle" vs "triangular". i might add though that 三角 can refer to a specific
triangle sketched on a piece of paper or blackboard in the sense that you can
say "look at this 三角 i just drew, its prettier than yesterday's 三角". but 三角形
doesn't have that power to specify one triangle among others, its referent is
just ambiguously the whole class of triangles.
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2012-08-07T09:46:13.627
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As Gradius said, the mathematical term “triangle” is 三角形, and never 三角. As
part of compound words, 三角 also appears; an example is 三角関数 (trigonometric
functions).

(As for the use of 三角 in compounds words, I think that there is a general
tendency to prefer to two-kanji words than three-kanji words when they are
used adjectivally in compound words. See also Chocolate’s comment on the
question “[What is the difference between 日曜日 and
日曜?](https://japanese.stackexchange.com/questions/6368/what-is-the-difference-
between-%E6%97%A5%E6%9B%9C%E6%97%A5%E3%80%90%E3%81%AB%E3%81%A1%E3%82%88%E3%81%86%E3%81%B3%E3%80%91and-%E6%97%A5%E6%9B%9C%E3%80%90%E3%81%AB%E3%81%A1%E3%82%88%E3%81%86%E3%80%91)”
by BabyAzerty.)

As a non-technical word, 三角形 is more formal and 三角 is less formal. I do not
recognize any difference in their meanings.
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2012-08-08T02:40:48.267
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