Re: Forcing a Derivative

*To*: mathgroup at smc.vnet.net*Subject*: [mg50765] Re: [mg50753] Forcing a Derivative*From*: Andrzej Kozlowski <andrzej at akikoz.net>*Date*: Sun, 19 Sep 2004 21:39:21 -0400 (EDT)*References*: <200409190756.DAA17973@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

On 19 Sep 2004, at 16:56, Scott Guthery wrote: > *This message was transferred with a trial version of CommuniGate(tm) > Pro* > How does one force Derivative[n] to actually take the derivative? > > For example if ... > > f[x_] = x^2 + 7 > > g[x_]=3x^3 + 23 > > then > > Derivative[2][f * g] > > just puts a couple of primes on the product rather than actually > computing the dervative. > > Thanks for any insight. > > Cheers, Scott > > Mathematica does not understand that you mean by f*g the function that takes x to f(x)*g(x). There are various ways to deal with this issue, but the simplest are: Derivative[2][f[#]*g[#] &][x] // Expand 60*x^3 + 126*x + 46 or Expand[D[f[x]*g[x], {x, 2}]] 60*x^3 + 126*x + 46 Andrzej Kozlowski Chiba, Japan http://www.akikoz.net/~andrzej/ http://www.mimuw.edu.pl/~akoz/

**Follow-Ups**:**Re: Re: Forcing a Derivative***From:*Murray Eisenberg <murray@math.umass.edu>

**References**:**Forcing a Derivative***From:*"Scott Guthery" <sguthery@mobile-mind.com>