My Math Forum The Protractor - Its Construction

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 April 19th, 2013, 07:57 AM #1 Banned Camp   Joined: Feb 2013 Posts: 224 Thanks: 6 The Protractor - Its Construction This topic is a continuation of this topic. viewtopic.php?f=13&t=18374#p163581 Who invented the 360 degrees protractor? When? How? How is it possible to divide a circle into 360 parts? The only way I know how is to divide it down to 3 degrees, but no way to divide it down to 1 degree, not straight-edge-and-compass exact. So how are modern and ancient protractors marked exactly? Or is it exact?
 April 20th, 2013, 07:03 AM #2 Banned Camp   Joined: Feb 2013 Posts: 224 Thanks: 6 Re: The Protractor - Its Construction Why? My guess. Highest common multiple of constructible polygons. Triangle, Square, Pentagon, Hexagon. 3 x 4 x 5 x 6 = 360
 April 20th, 2013, 07:16 AM #3 Math Team   Joined: Apr 2010 Posts: 2,778 Thanks: 361 Re: The Protractor - Its Construction Do you mean the highest common multiple of 3, 4, 5 and 6?
April 20th, 2013, 07:32 AM   #4
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Re: The Protractor - Its Construction

Quote:
 Originally Posted by Hoempa Do you mean the highest common multiple of 3, 4, 5 and 6?
Yes. But those are are not just numbers. They are analog fractions of a circle.

 April 20th, 2013, 07:43 AM #5 Math Team   Joined: Apr 2010 Posts: 2,778 Thanks: 361 Re: The Protractor - Its Construction There are infinitely many numbers higher than 360 that are a multiple of 3, 4, 5 and 6.
 April 21st, 2013, 06:53 AM #6 Banned Camp   Joined: Feb 2013 Posts: 224 Thanks: 6 Re: The Protractor - Its Construction I found the answer. You can't draw 1 degree with straight edge and compass. viewtopic.php?f=13&t=18374&p=163757#p163757

### how to divide a circle into 360 parts without a portractor

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