Simplifying Limits for Functions of Several Variables

The idea that the limit for functions of several variables cannot be done by employing only one variable has been treated in the calculus courses as a myth or taboo. A very easy-to-prove theorem shows that, for a very large class of functions, this limit can be reduced to a limit done in only one variable, the radial variable of a system of spherical coordinates centered in the limit point. This theorem is very practical to make limits for functions of several variables with the help of softwares and should be included in any calculus' book. Then the student would employ this tool, already heuristically suggested in many books, but with certainty, knowing the precise conditions for it, without any danger of improper generalizations.