New to gcc: missing sin/cos

["Brian G. Neal" <bneal@ia.net>]

I am trying to port some C code from Windows (i.e. no
makefile) and I am using gcc for the first time.
One of the files has some sin() and cos() calls
in it. And yes it includes math.h. If I do a:

% gcc -o main main.c file1.c file2.c

I get some error messages about not finding sin and cos.

I assume I need to include some library that has sin/cos.
I found the -l switch to pass libraries to the linker but
I have no idea what library to use. Am I missing something
obvious here?

Any ideas? Thanks!!