RE: How do I pick out the expression under a radical?
- To: mathgroup at smc.vnet.net
- Subject: [mg36257] RE: [mg36225] How do I pick out the expression under a radical?
- From: "DrBob" <drbob at bigfoot.com>
- Date: Wed, 28 Aug 2002 04:16:18 -0400 (EDT)
- Reply-to: <drbob at bigfoot.com>
- Sender: owner-wri-mathgroup at wolfram.com
FullForm[expr] Plus[Times[a,b,Power[x,2]],Times[5,Power[x,3]], Times[5,Power[Plus[4,Times[-1,Power[x,2]]],Rational[1,2]]]] What you want is the third argument of Plus, the second argument of Times, and the first argument of Power. expr = a b x^2 + 5 x^3 + 5 Sqrt[4 - x^2]; expr[[3]] expr[[3, 2]] expr[[3, 2, 1]] 5*Sqrt[4 - x^2] Sqrt[4 - x^2] 4 - x^2 Bobby Treat -----Original Message----- From: Steve Beach [mailto:asb4 at psu.edu] To: mathgroup at smc.vnet.net Subject: [mg36257] [mg36225] How do I pick out the expression under a radical? I'm a poor physicist trying to figure out how to sort out the "physical" from the "non-physical" solutions to a problem. To do that, I need to be able to look at an expression and pick out a subexpression, the part under the radical. For example, say I've got the expression a b x^2 + 5 x^3 + 5 Sqrt[4 - x^2] I'd like to pick out "4 - x^2", which would then tell me that x is between +/- 2. I know there has got to be an easy way to do it, but I can't find it. Any help would be appreciated. Thanks, Steve Beach asb4 at psu.edu http://www.thebeachfamily.org