My Math Forum Constructing a 20 Degree Angle using Compass and Ruler Only
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 View Poll Results: Is this a useful construction? Yes 1 9.09% No 0 0% There are other ways 3 27.27% This method is wrong 7 63.64% Voters: 11. You may not vote on this poll

 April 21st, 2013, 08:34 AM #31 Banned Camp   Joined: Feb 2013 Posts: 224 Thanks: 6 Re: Constructing a 20 Degree Angle using Compass and Ruler O My Guess on the Cubic Nature of Angle Trisection http://www.flickr.com/photos/85937466@N ... otostream/ Straight edge and compass can only draw circles and perpendicular lines. Using only perpendicular lines, you can only create trigonometric relationships. Angle trisection involves finding the cube root of the cosine.
April 21st, 2013, 09:33 AM   #32
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Re: Constructing a 20 Degree Angle using Compass and Ruler O

Quote:
 Originally Posted by long_quach My Guess on the Cubic Nature of Angle Trisection http://www.flickr.com/photos/85937466@N ... otostream/ Straight edge and compass can only draw circles and perpendicular lines. Using only perpendicular lines, you can only create trigonometric relationships. Angle trisection involves finding the cube root of the cosine.
"The problem (trisection) of constructing an angle of a given measure ? is equivalent to construct
two segments such the ratio of their length is cos?.

... It follows that, given a segment that is sought as having a unit length, the problem of angle trisection is equivalent to construct a segment whose length is the root of a cubic polynomial " - Wikipedia.

https://en.wikipedia.org/wiki/Angle_trisection

Bingo!

 February 18th, 2017, 03:42 AM #33 Newbie   Joined: Feb 2017 From: India Posts: 1 Thanks: 0 Visit this link
 August 21st, 2017, 02:53 AM #34 Newbie   Joined: Jul 2016 From: Kenya Posts: 3 Thanks: 0 Construction of 20 degrees angle Hi guys. Please find out how to construct an angle of 20 degrees, 70 degrees, and other whole number angles from the youtube link: https://www.google.com/url?sa=t&rct=...YK25pwOlcIFuDQ. Thanks.

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# how to draw 20 degree angle with compass

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