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Re: construction of angles
Posted:
Mar 29, 1998 7:58 AM


rajuyr@giasbga.vsnl.net.in wrote: > > I KNOW HOW TO CONSTRUCT ANGLES LIKE 30,45,90,60 DEGREES BUT I ALSO > WANT TO KNOW HOW TO CONTRUCT 20 AND 50 DEGREES. I HOPE U SEND ME THE > METHOD TO ME AT MY EMAIL.
Rajuyr,
You may have heard that it is, in general, impossible to trisect an angle using compass and straightedge. Well, it happens that a 60 degree angle is impossible to trisect; that is, it is impossible to construct a 20 degree angle using the allowed tools. This means it is also impossible to construct a 50 degree angle as well (20 = 50  30, so if you could construct a 50 degree angle, you could construct a 20 degree angle, which you can't).
To understand WHY you can't construct a 20 degree angle, you need to understand some Galois theory. This is something I didn't learn until graduate school, and I don't know offhand of a good elementary treatment. Perhaps someone else in the forum will suggest a reference.
Peter



