Re: Calculating derivate in Mathematica 9 giving wrong result

*To*: mathgroup at smc.vnet.net*Subject*: [mg131444] Re: Calculating derivate in Mathematica 9 giving wrong result*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Sun, 7 Jul 2013 23:21:07 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-outx@smc.vnet.net*Delivered-to*: mathgroup-newsendx@smc.vnet.net

On 7/3/13 at 5:01 AM, jhlawley at gmail.com (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. You asked Mathematica to solve a different problem than what you asked WolframAlpha to solve Notice in the numerator of your In[5] above is x^2 - 2 while the numerator of what you sent to WolframAlpha is x^2 + x - 2 That is: In[2]:= D[((x^2 + x - 2)/(x^3 + 6)), x] // Together Out[2]= (-x^4 - 2*x^3 + 6*x^2 + 12*x + 6)/(x^3 + 6)^2