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Re: differentiate a function of a function


f[x_,y_]:=Tan[t[x,y]+a[x,y]];

D[f[x,y],x]

Sec[a[x, y] + t[x, y]]^2*
  (Derivative[1, 0][a][x, y] + 
   Derivative[1, 0][t][x, y])


Bob Hanlon

---- kem <kemelmi at gmail.com> wrote: 
> Hi,
> 
> I was wondering how do I define a function in mathematica to be able
> to differentiate it etc, where some of the parameters of this function
> should be also a function. For example I want to be able to do the
> following operations:
> 
> 1) to say that f is a function: f(x,y) = Tan[t(x,y)+a(x,y)]
> 
> 2) take D[f,x] , such that also t(x,y) and a(x,y) will be also
> differentiated
> 
> 3) be able to substitute these into some equation like: f_x f_xy = 8
> 
> Thanks a lot
> 
> kem
> 
> 



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