GCC link time errors calling trig functions

System:
Kubuntu 5.1 amd64
gcc version:
gcc (GCC) 4.0.2 20050808 (prerelease) (Ubuntu 4.0.1-4ubuntu9)

bob@johnket5:~/projects/plate_and_sheet$ gcc -Wall -o pands pands.c
/tmp/cckui0iR.o: In function `dome':
pands.c:(.text+0x6aa): undefined reference to `cos'
collect2: ld returned 1 exit status

What library do I need to link?

Thanks
Bob Parker