fsolve solves numerically, that is without parameters (which is analytical solution). If you have 4 equations you can solve numerically for 4 symbols. if x is not assigned a value or is not solved for (though then you will need another equation) then numerical solution is impossible to obtain.

Either assign x a value, or try to find an analytical solution.

I can suggest using the package: Student[VectorCalculus]. It allows an easy way to do this.

Try the following code:

with(Student[VectorCalculus]):

MapToBasis(<x,y,z>, 'cylindrical')

I also suggest that you take a look at other relevant functions in that package.