Looks like you've got the formulae the wrong way around - distance = chlong (minutes) x cos (mean latitude) whereas convergence = chlong (degrees) x sin (mean latitude).
Neither of these will give you the rhumb line direction between two points and if you're talking about ATPL level material you won't have to calculate that in an exam.
You may be given two points where the rhumb line direction is implied (e.g. they're on the same parallel of latitude) and you might be asked to calculate the GREAT CIRCLE track (intial, mid-way, and final) between the two.
Is there a specific question you're looking at?
Rgds,
V1R