Re: Calculating derivate in Mathematica 9 giving wrong result

• To: mathgroup at smc.vnet.net
• Subject: [mg131418] Re: Calculating derivate in Mathematica 9 giving wrong result
• From: Frank K <fkampas at gmail.com>
• Date: Wed, 3 Jul 2013 22:01:42 -0400 (EDT)
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• References: <kr0oo9\$3eu\$1@smc.vnet.net>

On Wednesday, July 3, 2013 4:52:25 AM UTC-4, James wrote:
> In[5]:= D[(x^2 - 2)/(x^3 + 6), x]
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> Out[5]= -((3 x^2 (-2 + x^2))/(6 + x^3)^2) + (2 x)/(6 + x^3)
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> That is from Mathematica 9.
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> The wolfram alpha site and my textbook give this answer:
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> d/dx((x^2+x-2)/(x^3+6)) = (-x^4-2 x^3+6 x^2+12x+6)/(x^3+6)^2
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> Please tell me what I am doing wrong.

Your input to Mathematica is not the same as your input to Wolfram Alpha.  x*x -2 is the numerator for your input to Mathematica.  Your input to Wolfram Alpha is x*x +x -2

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