In cryptography (and probably in many other areas) there is a huge usage of negligible functions when proving theorems.
Although I know what is a negligible function, every time I encounter a function that need to be determined as negligible or not I just don't know how to do that. I just say that the function is negligible if it seems like $c/2^n$ where $c$ is a constant (or known to be negligible).
Can you provide an efficient method to determine quickly if a function is negligible or not?