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Re: Calculating derivate in Mathematica 9 giving wrong result


On 7/3/2013 3:52 AM, James wrote:
> In[5]:= D[(x^2 - 2)/(x^3 + 6), x]
>
> Out[5]= -((3 x^2 (-2 + x^2))/(6 + x^3)^2) + (2 x)/(6 + x^3)
>
> That is from Mathematica 9.
>
> The wolfram alpha site and my textbook give this answer:
>
> d/dx((x^2+x-2)/(x^3+6)) = (-x^4-2 x^3+6 x^2+12x+6)/(x^3+6)^2
>
> Please tell me what I am doing wrong.
>

but
        D[(x^2 - 2)/(x^3 + 6), x]

is not the same as

       d/dx(  (x^2+x-2)/(x^3+6)  )

you have an extra 'x' in the Alpha example.

--Nasser




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