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Re: How do I create a parametric expression?

• To: mathgroup at smc.vnet.net
• Subject: [mg68595] Re: How do I create a parametric expression?
• From: axlq at spamcop.net (axlq)
• Date: Fri, 11 Aug 2006 04:40:06 -0400 (EDT)
• References: <ebebnc$lg7$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

In article <ebebnc$lg7$1 at smc.vnet.net>, David Park <djmp at earthlink.net> wrote:
>expr /. (q - z)^2 -> r^2 - a^2
>FullSimplify[%, r > 0]
>% /. r -> Sqrt[a^2 + (q - z)^2]
>Simplify[%, a < 0]
>
>I don't know if you can assume that r > 0. You will probably get a better
>answer from the algebraists in the group.

Thanks David.  In my case, I *know* R>0, a>0 always.

-Alex