1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Abstract Algebra Question dealing with Constructible Numbers

  1. Nov 6, 2011 #1
    1. The problem statement, all variables and given/known data

    Let c=cos(2pi/5). It can be shown that (4c^2)+(2c)-1=0. Use this fact to prove that a 72degree angle is constructible.

    2. Relevant equations



    3. The attempt at a solution

    I can see that using the equation and what c equals that you get the statement 0=0 and I know that 2pi/5 relates to 72degree angle on the unit circle but I have no idea how to formally prove it. Also can equate cos(2pi/5) but don't see how that would help either.
     
  2. jcsd
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?



Similar Discussions: Abstract Algebra Question dealing with Constructible Numbers
  1. Abstract Algebra (Replies: 0)

Loading...