Given any angle how can you say that it is constructable or not?
geometric construction of a given angle
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euclidean-geometry
field-theory
galois-theory
geometric-construction
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1How are you given the angle? – 2011-05-01
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4You have read [this](http://en.wikipedia.org/wiki/Compass_and_straightedge_constructions#Constructible_angles), yes? – 2011-05-01
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2J.M.'s link will undoubtedly help you move towards your question. But just a reference if you want a nice soft introduction is Howie's Fields and Galois Theory. I find his treatment of constructibility to be very nice. However I notice that Dinesh added the (relevant) tag "field-extensions". Which means I don't know your background. You should edit your question to include more information about your background so that we can help you more than pointers to resources(or at least make sure those pointers are the right pointers). – 2011-05-01
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0Please use meaningful titles. – 2011-05-02