The answer is that you can provide prefix-arguments to such functions; this can be done in two ways:
- positive numeric arguments can be specified with M-<number>; that is, to use 5 as the prefix argument, you'd type M-5;
- any numeric argument can be specified using C-u; so to set -3 as the prefix argument, you'd type C-u -3. Some functions also take C-u as a kind of boolean parameter; you set the parameter by specifying C-u without any parameter.
Note: after ten years of using emacs, I discovered the M-<number> notation only when writing this entry...