There are my 'two cents' to a discussions about 'right angles'. I decided to store it in history (LOL) as it took pains for me to write it. (words in italics are not mine!)

N1:

Maths is not my cup-of-tea, nevertheless, I'd like to make it clear: a right angle means 90 degrees or п/2 radians, as I've posted in the comment.

"The article that you’ve proposed me to look trough is good one." - if it's in fact so, then one may read there:
"A right angle may be expressed in different units:
* 90°
* π/2 radians"

"Unfortunately, you have understood that article wrong." - What you mean to say is that I failed to understand the article. Actually, I had no intention to go deep into trigonometry, I just read and copied the facts. For example "π radians = 180 degrees" - don't you agree? In case you do, what about 'half-п radians'?


"One radian is equal to 180/π(or 360/2π degrees, or about 57.2958 degrees." - I am not going to deny anything so obvious, the only thing worth pointing out is that I didn't write about radians, but about degrees.

"It comes about right angle but not about plane one!" - that is a true enigma for me! Aren't we dealing with a right angle?! Humbly, I must confess, I failed to understand what you meant here. Will you kindly give a synonym to 'come about'?

"Please count what will you get having dividing π by 2 radians! 3,14 : 114,58° = ???" - I actually find counting rather dull and boring though I have to do it pretty often. I have a calculator, besides I can also do the sums by myself. If you insist, I may say the answer is - 0,0274. Will you kindly tell me what we are counting here and in what units: degrees, radians, or...?

"I think, now you’ve caught the sense." - you are flattering again. In fact, nothing of that kind. My English seems to be good enough to read authentic texts, though it fails to get what you are aiming at.


I am grateful to you for drawing my attention to Maths and trigonometry once again. I was rather proud to realise that I had been a good pupil at school, though Maths is not connected with my profession now.
Now that I've studied the whole matter about angles, radians and degrees once again (thanks to wikipedia), I insist on the following:
2п radians = 360 degrees
п radians = 180 degrees
п/2 radians = 90 degrees - that's quite the thing I wrote in the comment.

Just in case you don't agree again, will you read: en.wikipedia.org/wiki/Radian

I would never say a word about Maths in Russian as I consider it awfully dull. The only excuse for me now is that I am using English in that case.

p.s. I really hope that the whole matter is obvious now.


N2:

I'm glad to have this question settled as it took me quite a lot of time to get concentrated on such things.

Anyway, now I might say I can teach Maths in English - lol

p.s. It's very human to get mistaken. Personally, I am not attentive and tend to make lots of mistakes, typos, illogical conclusions and what not. So, I've searched the Internet for a good check-your-spelling machine, a dozen of profound dictionaries, a number of reliable encyclopedie (wikipedia being my favourite as it is highly understandable) and I got them both on- or out-line. They truly save much of my time and emotions though I still keep making mistakes.

p.p.s. the word 'plane' is highly polysemantic; in Maths it denotes 'surface' and in so-to-say everyday life its synonym is 'valley'. The word originates from Latin 'planum' which means 'flat surface'. That might be one of the reasons for calling 'airplane' as something 'moving along flat surface in the air'. I bet, ABBY fails to provide such information about a word, that's why I stopped using it ages ago.

As for 'the angle between two planes (if you mean this one by 'plane angle' it is most usually called a dihedral angle. I quite believe you they might have some other features. I just have no intention of diving into trigonometry more then I have already done.


I've done it!