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Replies: 24   Last Post: Jan 8, 2007 9:09 PM

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 Dave L. Renfro Posts: 4,792 Registered: 12/3/04
Re: simplify radicals - regular 12-gon
Posted: Dec 22, 2006 1:05 PM

Dave L. Renfro wrote (in part):

> THEOREM: Let p,q be rational numbers. Then sqrt(p +/- sqrt(q))
> can be expressed as sqrt(a) +/- sqrt(b) for some
> rational numbers a,b if and only if p > 0 and p^2 - q
> is a perfect square.

This should begin with "Let p,q be nonzero rational numbers such
that sqrt(q) is irrational". Chrystal doesn't say this in his
statement of the result, but these assumptions probably appear
a few pages earlier. Note to anyone writing a book or planning
to write a book: To increase the value of your book as a
reference, key results should be stated as much as possible in
a way that is "locally correct" and "locally understandable".

Dave L. Renfro

Date Subject Author
12/20/06 lite.on.beta@gmail.com
12/20/06 Pubkeybreaker
12/20/06 lite.on.beta@gmail.com
12/20/06 G. A. Edgar
12/21/06 Stan Brown
12/21/06 JEMebius
12/22/06 Dave L. Renfro
12/22/06 Dave L. Renfro
12/22/06 G. A. Edgar
12/23/06 Dave L. Renfro
12/20/06 Dave L. Renfro
12/20/06 Pubkeybreaker
12/20/06 Dave L. Renfro
12/20/06 Nat Silver
12/21/06 Pubkeybreaker
12/20/06 Iain Davidson
12/20/06 Iain Davidson