Re: Trisecting an angle
- From: Arturo Magidin <magidin@xxxxxxxxxxxxxx>
- Date: Sat, 25 Jul 2009 11:41:28 -0700 (PDT)
On Jul 24, 11:28 pm, qsymmetry <qsymme...@xxxxxxxxx> wrote:
On Jul 24, 10:34 pm, qsymmetry <qsymme...@xxxxxxxxx>
wrote:
suppose A is an angle between 0 and 90 degrees, and
cos A = 1/5.
Why can't A be trisected with a straightedge andcompass ?
Do you know the criteria for knowing whether a number
can be
constructed with a straightedge and a compass in
terms of its
algebraic degree? If not, then you won't be able to
understand the
question without a lot of material.
the degree of Q(a)/Q must be a 2-power if
a is constructible.
in this instance, the cos is throwing me off. ;(
You might have mentioned that to begin with. (HINT: Do start saying
what you have tried and why you are stuck, as opposed to simply
posting the question. Show that you are actually working at the
problems before posting, and giive potential posters an idea of why
you are stuck and what your level is. So far, you give the strong
impression of someone who is too lazy to think about the problems
himself and would much rather have the newsgroup do his homework for
him).
An angle is constructible if and only if its cosine is constructible,
if and only if its sine is constructible. Now use the triplication
formulas.
--
Arturo Magidin
.
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