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Re: Newbie Question: Solving for x?

• To: mathgroup at smc.vnet.net
• Subject: [mg40707] Re: [mg40681] Newbie Question: Solving for x?
• From: Dr Bob <majort at cox-internet.com>
• Date: Mon, 14 Apr 2003 04:05:53 -0400 (EDT)
• References: <200304130618.CAA27351@smc.vnet.net>
• Reply-to: majort at cox-internet.com
• Sender: owner-wri-mathgroup at wolfram.com

Clear[x, y, f]
Off[Solve::ifun]
Solve[y == 1/(E^(x^2/2)*Sqrt[2*Pi]), x]

{{x -> (-I)*Sqrt[2]*Sqrt[Log[Sqrt[2*Pi]*y]]}, {x -> 
I*Sqrt[2]*Sqrt[Log[Sqrt[2*Pi]*y]]}}

Here's a derivation of sorts:

y == 1/(E^(x^2/2)*Sqrt[2*Pi])
Sqrt[2*Pi]# & /@ %
Log /@ % /. Log@Exp@a_ :> a
-2# & /@ %
Sqrt /@ % /. Sqrt[a_^2] :> a
x == ±First@%

Bobby

On Sun, 13 Apr 2003 02:18:14 -0400 (EDT), AngleWyrm 
<no_spam_anglewyrm at hotmail.com> wrote:

> I have a formula expressing y in terms of x:
>
> \!\(y = \[ExponentialE]\^\(\(-x\^2\)\/2\)\/\@\(2  \[Pi]\)\)
>
> How do you make it so that it expresses x in terms of y?
>
>
>



-- 
majort at cox-internet.com
Bobby R. Treat

• References:
  • Newbie Question: Solving for x?
    • From: "AngleWyrm" <no_spam_anglewyrm@hotmail.com>