very little to a lot. All depends on the game, the language/engine and what you want to do. If you just write game logic, you will need less math than when writing an engine to handle gfx code (unless you write a RPG with complex math based rules, or you write some clever AI system (but that's more algorithms than formula…
FWIW I don't think C++ is a good choice for a beginner or someone who wants to make games quickly on their own. The performance benefit of C++ is unlikely to be needed since lone developers are not going to be able to churn out full AAA games on their own. Enough performance can be had with just about anything else these…
The short answer is yes, though in many ways it's much more roundabout to get a game working in Actionscript than Unity. You're basically starting from scratch and building up a game from there, though you don't have to go as low level as something like C++. Most of the really complicated things are taken care of for you…