Is the ratio of two concave functions concave, convex, quasi-concave?
What does it depend on?
https://math.stackexchange.com/ may be more appropriate for questions as to what functions are concave, convex, quasi-convex, etc. You should already know the status of functions you are implementing an an optimization model in CVX. Nevertheless, if you spend a few moments playing around with some simple functions, certain things should quickly become obvious.