Coming out with "clean" values for arccos, arcsine and arctan 1. The problem statement, all variables and given/known data Not so much a homework problem just something that bugs me and it's taken until first year Uni math before I asked it. In the text or in lectures when taking the arccos of say, 1/root2, the lecturer won't write 0.7853..., but rather a very nice looking pi/4. How does s/he know this? It seems like they know a "nice" way of writing every arc function value. At the moment I need arccos(3/5), what about this one, is there a nice way of writing this? Instead of 0.927... Cheers.