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Topic: Prove that 2Cos(2pi/7) is a root to x^3+x^2-2x-1.
Replies: 1   Last Post: Sep 12, 2006 3:23 PM

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Jason Fahy

Posts: 15
From: Edmonton, AB
Registered: 9/5/06
Re: Prove that 2Cos(2pi/7) is a root to x^3+x^2-2x-1.
Posted: Sep 12, 2006 3:03 PM
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I'm trying something involving a half-angle identity; I'll let you know if I get anywhere with it.

Edit: I got a few terms to cancel using cos^2 x = 1/2 + 1/2 cos 2x, but so far I haven't been able to finish it.

Message was edited by: Jason Fahy

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