Let R be an integral domain with identity element 1. Show that there at most two elements "a" in R such that a^2=1
The Attempt at a Solution
Being an integral domain implies that if ab=0, then a=0 or b=0. a^2=1 implies a=1. Then (a)(a) = (1)(1). This seems like a simple problem but I'm not sure how to properly state that there are "at most 2 elements."