# What is a "Radian"?

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#1
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Posted 09 July 2001 - 03:13 AM

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#3
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Posted 09 July 2001 - 03:43 AM

Degrees are the same deal but divided into 1/360th of a circle.

They both are simply units for measuring angles. You can choose either and convert either.

Remember how we have differant units of measure for lengths, meters, centimeters etc. We have differant units of measurment for angles to.

P.S. Its best to see a diagram in a math book to help you understand, just understand now that a radian is simply another way to measure an angle.

ECKILLER

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#4
Anonymous Poster_Anonymous Poster_*
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Posted 09 July 2001 - 03:44 AM

1 radian is equal to 180/pi degrees.

hope thats simpler for you.

Nomad

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#5
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Posted 09 July 2001 - 04:05 AM

Here are some simple degree -> Radian equalities.

DEGREES RADIANS

360 2PI

270 3PI/2

180 PI

90 PI/2

I hope this helps some.

-Will

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#6
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Posted 09 July 2001 - 08:43 PM

sin(x) = x - x^3/3! + x^5/5! - x^7/7!...

cos(x) = 1 - x^2/2! + x^4/4! - x^6/6!...

If you consider the unit circle, where the length along the arc of the circle is equal to the angle in radians, then you can see why that suits the trig formulas so well...

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#7
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Posted 10 July 2001 - 05:19 AM

Graham Rhodes

Senior Scientist

Applied Research Associates, Inc.

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#9
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Posted 11 July 2001 - 03:10 PM

*did*they choose 360 degrees for a complete circle? Does anyone know?

War Worlds - A 3D Real-Time Strategy game in development.

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#10
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Posted 11 July 2001 - 03:26 PM

Probably because it is evenly divisible by so many factors:

2 x 2 x 2 x 3 x 3 x 5 = 360

I don''t know when 360 was first in common use, but I think it had something to do with numerology.

Bottom line is they had to pick something.

The thing is, if you don''t like 360, you can divide your circle into as many "degrees" as you want. Personally, in my programming, I usually use 3600 "degrees" in a circle.

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#11
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Posted 11 July 2001 - 03:33 PM

Oh, and Beer Hunter, those are NOT actual formulas for sine and cosine, but rather they are Power Series approximations. Exact formulas for sine and cosine can only be written using Complex exponential functions.

quote:Original post by Dean Harding

Whydidthey choose 360 degrees for a complete circle? Does anyone know?

The 'Grooved Ware' people used (some 5000-10000 years ago) a system of measurement for time, distance and angle that were all based on the same base number set that had 366 'degrees' in a full circle, 60 'minutes' per 'degree' and 6 'seconds' per 'minute'. Of course, these 'degrees', 'minutes' and 'seconds' were not of the same length as the ones we use, hence the quotes to indicate this.

Using these numbers, then the distance subtended on the Earth's surface by 1 'second' of rotation of the Earth is 366 Megalithic yards (called a Megalithic Mile). From here you can see that distance can be computed in terms of rotation angle subtended on the surface of the Earth and this corresponds to a time taken to rotate through that angle/distance. This was a fantastically beautiful system of measurement.

Unfortunately, (I'm not sure but seem to recall that it was caused by a merging of the Zedokite and Cannonite religions) this number system was abolished in favour of the 360, 60, 60 system of time and angle, which was far easier to deal with. Unfortunately, this meant that distance was 'knocked out' of the combined system and hence we now have a rather

*ad hoc*distance measurement scheme (two in fact, Imperial and Metric). If you want more information about the Pre-History of Science, check out "Urial's Machine". I cannot recall the authors right now, but will chase them up if needs be (I've loanded my copy to a friend... great book!!!!).

Cheers,

Tim

Edited by - Timkin on July 11, 2001 10:36:19 PM

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#13
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Posted 11 July 2001 - 03:43 PM

A radian is equal to the circle''s radius. That''s all. It''s not an arbitrary measurement, nor was it chosen to simplify the math equations. It''s just said to be equal to a circle''s radius. Thus, since the circumference of a circle is 2*pi*Radius, there are 2*Pi radians in a circle.

~CGameProgrammer( );

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#14
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Posted 11 July 2001 - 09:45 PM

That''s the thing I wanna hear, pal!!!!!!!! WHOA!!!!!!!!!!!!!! How simple and easy to understand, pal!!!!!!!!!!!!!!!!!!! :-D HEE-HAW!!!!!!!!!

So, that means if the radius is 4 , then the Radian is also 4 too, right? :-D THAnKS!!!!!!!!

"The feeling of mastering and understanding hard stuff in Game Programming is just like the feeling u get when u perform an Air-Walk in the basketball court, soaring.....and everyone''s watching in awe......."

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#15
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Posted 12 July 2001 - 03:56 AM

CGameProgrammer, you did write an incorrect thing when you said "A radian is equal to the circle''s radius." Not so. I think you may have written this carelessly. You actually disproved your own statement when you took the Radius out of your equation "2*pi*Radius" to arrive at 2*pi radians in a circle.

In actuality, the other explanations here are correct. Radians really do exist, as Beer Hunter said, because of the Taylor series expansions. These particular expansions are called the Maclaurin expansions:

http://www.xrefer.com/entry.jsp?xrefid=645374

The term radian seems to have appeared first in 1873 with regard to these expansions:

http://sunsite.utk.edu/math_archives/.http/hypermail/historia/mar00/0012.html

Now, as to the formula 2*pi*Radius for the circumference of a circle, well that''s just a side effect really, since the points on a circle can be constructed *using* 1 full wave of the sin(x) and cos(x) functions, which have a *wavelength* of 2*pi radians.

Graham Rhodes

Senior Scientist

Applied Research Associates, Inc.

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#16
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Posted 12 July 2001 - 02:38 PM

quote:Original post by grhodes_at_work

Radians really do exist, as Beer Hunter said, because of the Taylor series expansions. These particular expansions are called the Maclaurin expansions:

Radians don''t exist ''because'' of the power series approximation, but rather the power series approximation is possible because of the nature of the radian measure.

It is certainly the case the the unit angle was used long before it was called a radian and long before a Maclaurin series was used to approximate trigonmetric functions of functions of unit angles.

...on a similar vein. While it is widely believed that Hipparchus was the founder of trigonometry in the 2nd century BC, it is more than likely that he, like Pythagorus, got his information from more ancient texts (scrolls). As some circumstantial evidence, if you measure the distance around the base of the great pyramid (Pyramid of Khafra) and divide it by its height, you get a number that matches 2*pi to several decimal places. If you perform the same calculation for the Pyramid of the Sun in South America (Tiahanucan (sp?) I think) you get 4*pi. I also seem to recall that the angle subtended by an edge of the Great Pyramid with the base is equal to the unit angle (1 radian). These pyramids were purposefully built to encapsulate these numbers. It is structurally more difficult to build a square based pyramid with these properties than it is to build a uniform sqare based pyramid (45 degree sides).

Regards,

Tim

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#17
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Posted 12 July 2001 - 03:40 PM

quote:Original post by Timkin

[quote]Original post by grhodes_at_work

Radians really do exist, as Beer Hunter said, because of the Taylor series expansions. These particular expansions are called the Maclaurin expansions:

Radians don''t exist ''because'' of the power series approximation, but rather the power series approximation is possible because of the nature of the radian measure.

It is certainly the case the the unit angle was used long before it was called a radian and long before a Maclaurin series was used to approximate trigonmetric functions of functions of unit angles.

Heh, heh...your statement is more accurate. Point taken!

quote:Original post by Timkin

...on a similar vein. While it is widely believed that Hipparchus was the founder of trigonometry in the 2nd century BC, it is more than likely that he, like Pythagorus, got his information from more ancient texts (scrolls). As some circumstantial evidence, if you measure the distance around the base of the great pyramid (Pyramid of Khafra) and divide it by its height, you get a number that matches 2*pi to several decimal places. If you perform the same calculation for the Pyramid of the Sun in South America (Tiahanucan (sp?) I think) you get 4*pi. I also seem to recall that the angle subtended by an edge of the Great Pyramid with the base is equal to the unit angle (1 radian). These pyramids were purposefully built to encapsulate these numbers. It is structurally more difficult to build a square based pyramid with these properties than it is to build a uniform sqare based pyramid (45 degree sides).

I actually love this kind of historical study, ancient civilizations, ancient astronauts and stuff. Maybe they didn''t call them by the *term* "radians" though! Lets not get into an argument about how old the pyramids in Egypt are, though!

Graham Rhodes

Senior Scientist

Applied Research Associates, Inc.

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#18
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Posted 12 July 2001 - 03:41 PM

quote:Original post by Timkin

Radians don''t exist ''because'' of the power series approximation, but rather the power series approximation is possible because of the nature of the radian measure.

It is certainly the case the the unit angle was used long before it was called a radian and long before a Maclaurin series was used to approximate trigonmetric functions of functions of unit angles.

Heh, heh...your statement is more accurate. Point taken!

quote:Original post by Timkin

...on a similar vein. While it is widely believed that Hipparchus was the founder of trigonometry in the 2nd century BC, it is more than likely that he, like Pythagorus, got his information from more ancient texts (scrolls). As some circumstantial evidence, if you measure the distance around the base of the great pyramid (Pyramid of Khafra) and divide it by its height, you get a number that matches 2*pi to several decimal places. If you perform the same calculation for the Pyramid of the Sun in South America (Tiahanucan (sp?) I think) you get 4*pi. I also seem to recall that the angle subtended by an edge of the Great Pyramid with the base is equal to the unit angle (1 radian). These pyramids were purposefully built to encapsulate these numbers. It is structurally more difficult to build a square based pyramid with these properties than it is to build a uniform sqare based pyramid (45 degree sides).

I actually love this kind of historical study, ancient civilizations, ancient astronauts and stuff. Maybe they didn''t call them by the *term* "radians" though! Lets not get into an argument about how old the pyramids in Egypt are, though!

Graham Rhodes

Senior Scientist

Applied Research Associates, Inc.

Graham Rhodes

Senior Scientist

Applied Research Associates, Inc.

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#19
Members - Reputation: **546**

Posted 12 July 2001 - 03:54 PM

quote:Original post by Timkin

The ''Grooved Ware'' people used (some 5000-10000 years ago) a system of measurement for time, distance and angle that were all based on the same base number set that had 366 ''degrees'' in a full circle, 60 ''minutes'' per ''degree'' and 6 ''seconds'' per ''minute''. Of course, these ''degrees'', ''minutes'' and ''seconds'' were not of the same length as the ones we use, hence the quotes to indicate this.

Wow! That''s a really great explanation! I love little bits of trivia like this.

Hehe, Megalithic Mile - it sounds very science fiction

War Worlds - A 3D Real-Time Strategy game in development.

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#20
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Posted 12 July 2001 - 08:48 PM

quote:Original post by grhodes_at_work

Lets not get into an argument about how old the pyramids in Egypt are, though!

No argument! They''re at least as old as 10450 BC give or take about 50 years... that''s the year in which there''s a natural astronomical (no, not astrological) alignment that matches the geographical alignment of many monolithic engineering feats of the era.

But more conclusively, there is much evidence to suggest that the Great Pyramid was already thousands of years old when Khafra had his face carved into the Sphinx around 2500 BC.

Additionally, the pit the Sphinx is carved into shows precipitation erosion only possible around 8000 years ago... and the direction the Sphinx is facing happens to align perfectly with the point on the horizon that the sun rises at on the first day of the age of Leo (i.e., the first time the suns precession causes it to rise in the constellation of Leo...and remember that the Sphinx is a lion)... and the year the sun first rose in Leo was... 10450 BC (give or take about 5 years)!!!

Freaky huh???!!!

Cheers,

Tim