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