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MathGroup Archive 2005

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Re: Convincing Mathematica that Sqrt[a+b]Sqrt[a-b]==Sqrt[a^2+b^2]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg63312] Re: Convincing Mathematica that Sqrt[a+b]Sqrt[a-b]==Sqrt[a^2+b^2]
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Fri, 23 Dec 2005 05:08:35 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

On 12/20/05 at 11:35 PM, hattons at globalsymmetry.com (Steven T.
Hatton) wrote:

>Is there a way to convince Mathematica to multiply
>Sqrt[a+b]Sqrt[a-b] to produce Sqrt[a^2+b^2]?  

Well there is:

In[1]:=
z = Sqrt[a + b]*Sqrt[a - b]; 
Sqrt[Expand[z^2]]

Out[2]=
Sqrt[a^2 - b^2]

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