       Re: Grouping terms under the radical

• To: mathgroup at smc.vnet.net
• Subject: [mg120106] Re: Grouping terms under the radical
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Fri, 8 Jul 2011 04:54:50 -0400 (EDT)
• Reply-to: hanlonr at cox.net

```You could use \$Post to apply the substitution to all output; however, ReleaseHold would not work without first clearing \$Post  since the substitution would be automatically reapplied to the output of the ReleaseHold.

mySqrt = # /. Sqrt[x_]*Sqrt[y_] -> HoldForm[Sqrt[x*y]] &;

\$Post = mySqrt;

expr = Sqrt[2 n]

HoldForm[Sqrt[2*n]]

\$Post =.

expr // ReleaseHold

Sqrt*Sqrt[n]

Perhaps easier to just apply mySqrt as required.

expr // mySqrt

HoldForm[Sqrt[2*n]]

Bob Hanlon

---- Paul von Hippel <paulvonhippel at yahoo.com> wrote:

=============
Thanks for this solution! But what if the expression Sqrt[2*n] is not something that I've input, but part of an expression in Mathematica's output. The output shows 2 and n under separate radicals. How can I tell the software I prefer to see terms combined under a common radical?

--- On Thu, 7/7/11, Bob Hanlon <hanlonr at cox.net> wrote:

From: Bob Hanlon <hanlonr at cox.net>
Subject: [mg120106] Re: Grouping terms under the radical
To: "paulvonhippel at yahoo" <paulvonhippel at yahoo.com>, mathgroup at smc.vnet.net
Date: Thursday, July 7, 2011, 7:25 AM

expr = Sqrt[2*n]

Sqrt*Sqrt[n]

expr /. Sqrt[x_] Sqrt[y_] -> HoldForm[Sqrt[x*y]]

HoldForm[Sqrt[2*n]]

% // ReleaseHold

Sqrt*Sqrt[n]

Bob Hanlon

---- paulvonhippel at yahoo <paulvonhippel at yahoo.com> wrote:

=============
This must be a classic question. When I input
Sqrt[(2 n)]
Mathematica displays the output as Sqrt Sqrt[n] -- i.e., both 2 and
n are under their own radical. The display of output doesn't change if
I impose the assumption that n > 0.

This is fine from a mathematical point of view, but it looks
unconventional when pasted into a paper. It seems to me most authors
would keep the 2 and the n under a common radical -- how can I get
Mathematica to do the same?

Thanks!

```

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