extracting unique values between 2 sets/files

Question

Working in linux/shell env, how can I accomplish the following:

text file 1 contains:

1
2
3
4
5

text file 2 contains:

Answer 1

here's another awk solution

$ awk 'FNR==NR{a[$0]++;next}(!($0 in a))' file1 file2
6
7