It sounds like an ATPL paper.
AFAIK, no JAA PPL or JAA IR syllabus has any mach number related stuff in it; they were removed within the past year or so. I certainly did not do any of this for the JAA IR7-exam set.
Maybe JAA CPL, or you are doing the whole JAA ATPL 14-exam set.
Maybe in France the 7 JAA IR exams are simply a subset of the 14 ATPL exams, which AIUI used to be the case in the UK also, until ~ 10 years ago, so maybe the French IR exams do indeed contain this dross.
Much as I hate to say this, the silly circular slide rule is good for this kind of stuff because you just line up the numbers you are given and read off the one(s) you are not given. I have a little Jepp CR-5 which does this.
One never does these calcs in real life.
why would I want to know my TAS?
In modern flying you don't really need to know it, because what matters is the GS, the ETE, the fuel flow, and the LFOB, and you get these off the GPS linked to the fuel totaliser
The TAS is useful if you want to work out roughly what the wind is when you are flying, by comparing the GPS GS with the TAS. But again without a GPS (or getting a DME GS reading
if flying more or less direct to/from a DME) that's not much good, either
But on any half decent speedo there is a subscale where you set the current altitude and OAT and you read the TAS straight off
