       Re: Simplifying with positive constants

• To: mathgroup at smc.vnet.net
• Subject: [mg26096] Re: [mg26062] Simplifying with positive constants
• From: Tomas Garza <tgarza01 at prodigy.net.mx>
• Date: Tue, 28 Nov 2000 01:55:40 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

```As I pointed out in my reply to your message [mg26060] something can be
done if you know that a, r, and d are positive real (by the way, in your
message there is a right parenthesis missing so my answer below may not
correspond to your actual question, but the idea is the same, of
course):

In:=
(1/2(r*a - a*d - Sqrt[4*r*a^2*d + (-r*a + a*d)^2]) /. {a -> Abs[a],
r -> Abs[r], d -> Abs[d]} // Simplify) /. {Abs[a] -> a,
Abs[r]->r,
Abs[d] -> d}

Out=
-a d

Tomas Garza
Mexico City

<djago at my-deja.com> wrote:

> I'm trying to calculate some results and when I evaluate them I get:
> 1/2(r*a-a*d-Sqrt[4*r*a^2*d+(-r*a+a*d)^2]
>
> I know that this is a complicated way of saying:
> r*a
>
> but Mathematica (3.0) doesn't seems to get the idea...
>
> I've tried with FullSimplify and so on... but Mathematica won't let a
> go out of the Sqrt function. Maybe If I could tell Mathematica that a,
> r and d are real and positive values...
>
> Can somebody give me a hint of how to do this???

```

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