Proving an Angle Cannot Be Trisected w/ Compass & Ruler

[murshid_islam]

i have read that it has been proven that an angle cannot be trisected using just a compass and a straight-edge (unless it is some specific angle, e.g., 90 degrees or 180 degrees). can anyone tell me where i can find the proof? can anyone suggest any website?

 

[arildno]

Buy an introductory book in algebra&group theory.

 

[dextercioby]

http://www.geom.uiuc.edu/docs/forum/angtri/

http://www.jimloy.com/geometry/trisect.htm

 

[ssd]

i have read that it has been proven that an angle cannot be trisected using just a compass and a straight-edge (unless it is some specific angle, e.g., 90 degrees or 180 degrees). can anyone tell me where i can find the proof? can anyone suggest any website?

If you are allowed to mark the straight edge with a pencil, then you can certainly trisect any acute angle. Of course, with marking not permitted you cannot.