Genghis,
I suspect we are talking about different graphs. I do not mean the rather complicted curves ones found in aerodynamic/engineering manuals. These are okay for the heavy stuff but are too much for students doing the JAR ATPL POF exams.
The ones I mean are simply straight lines indicating the general efects of climbing and descending.
The one for use below the tropopause in the ISA uses three straight lines spreading out in a fan shape fom the same point at the bottom. These are marked C (for CAS), T (for TAS) and M (for Mach number) from left to right. The speed scale increases from right to left, and the altitude vertically upwards.
To find the effect of climbing at constant CAS, TAS or Mach, simply rotate the fan so that your constant value is vertical. The other lines then indicate how the other two variables change. Climbing at constant TAS for example causes CAS to decrease and Mach to increase.
The graph for use above the tropopause is even more simple. Because temp and LSS are constant, the mach number at any TAS is constant. This means that TAS and Mach are indicated by a single line. Climbing above the tropopause at constant CAS for example, causes TAS and mach number to increase.
To determine the effects when descending simply move down the graph and observe how the lines converge.
These graphs can also be used to deternmine how flight through an inversion or isothermal layer affects speeds, provided you remember what we have both said about these phenomena. (temp lapse is reversed in an inversion and temp is constant in an isothermal). This means that as far as the
ratios of speeds goes, flight in an isothermal is like flight above the tropopause (only two lines on the graph) and for flight in an inversion just go in the opposite direction on the three line graph.
Your equation for mach number/LSS is probably a bit too much for the exams. In most cases it is enough to remember that the LSS is 38.94 x the square root of the absolute temperature.
The questions I provided in my previous post are intended to help students to develop skills in analysing these factors. Some of them (like many real exam questions) might appear to be lacking in information, but are in fact quite complete. In all cases there is only one best option. With the aid of the graphs I described above, each of the questions can be answered within a couple of minutes or less.