How to suppress a correct result? - A truly interesting question! In your example you are transforming for x
a function which does not depend on x
but on bx
. You probably meant:
FourierTransform[Cos[b x], x, k]
(* Out: Sqrt[\[Pi]/2] DiracDelta[-b+k]+Sqrt[\[Pi]/2] DiracDelta[b+k] *)
Again it contains this irritating Dirac-Deltafunction, but nevertheless this answer is correct. What would you like to get?
EDIT: @John: When I wrote the above I had not seen your response - sorry!