Upgrading from:

LinearAlgebra`FourierTrig`

New function FourierDCT has been added to the built-in Mathematica kernel.
New function FourierDST has been added to the built-in Mathematica kernel.

Evaluate the discrete Fourier cosine transform of Type I using FourierDCT[data,1]:

Version 5.2 << LinearAlgebra`FourierTrig`; data = Table[1 - 2 Abs[x - .5], {x, .1, .9, .1}]; FourierCos[data]

Evaluate the discrete Fourier sine transform of Type I using FourierDST[data,1]:

Version 5.2 FourierSin[data]