Why is a triangle not called a trigon, since a five sided geometrical shape is called a pentagon?

Question

Why isn't a triangle called a trigon? Why isn't a square called a quadrangle or a quadragon?

Answer 1

Why isn't 11 called oneteen, 12 twoteen? Why do you need the words "once" and "twice" in English when "x times" works perfectly for any x greater than 2? In French, there's no equivalent to the word "twice", we use "une fois", "deux fois", "trois fois" etc. But we have language quirks of our own, for example "quatre-vingts" ("four score") is universally used for the number 80.

Not all number language was invented by mathematicians...

Answer 2

The words triangle and square were in common use before conventions were formed for naming other types of polygons. The English language is a hybrid, taking common words from several different root sources. It's not formed acording to strict logic rules like a computer programming language. For that matter, a square is sometimes called a quadrangle, when referring to landscape features. Your question is more suited to a history of language discussion than to a math discussion, try it there and maybe you can get some specifics.

Answer 3

In fact, pentagonal is a variant of pentagon. [Check a dictionary.]

"..agonal" in fact means angle. So you are absolutely right, but someone has already thought of it before you. And, for consistency, it should remain triangle, but the pentagon should be pentagonal.

PS: Quadrangle is consistent with triangle...both have "angle" in them. A square is a quadrangle, but a quadrangle can be any four sided (or four angled) shape.

Answer 4

Tradition, I guess. Triangles are a lot more extensively studied than the other polygons, so over the ages they got their own name. It would be perfectly acceptable to call a triangle a trigon, if you wanted, and you could also call a square a tetragon.

Sincerely,


açafrã[e-mail]

Answer 5

My guess is that they named the triangle first, because mathematicians studied it first, and the name makes perfect sense when you think about it (even for rectangle, because they are right angles!).

But then they started studying shaped with more than four sides and they had to make up a way to name all polygones. The name also make sense, since it is diverted from greek polus (many) and gônia (angle).

They could have renamed the triangle and rectangle I guess, but scientific are found of tradition :-)

Answer 6

I guess because the general population started naming these shapes before the mathematicians took a hand.

Interestingly a pentangle is actually the five pointed star beloved by magicians which has in its centre a pentagon.

Answer 7

According to your logic a quadrilateral must be called a quadron. An angle which is one step lower than triangle must be called bion! Call it any thing. We must work the rules properly. Let us say the reason is convention agreed by most.

Answer 8

A seven sided form is called a chestahedron

Answer 9

Angles

Answer 10

good question, but then you have the, why is a 4 sided figure called a quadrilatical? (then theres the rhombus, trapaziod square, rectangle...)