How do you tell a fellow student they're wrong without sounding arrogant?
"But, I thought I read that the .............. " "I might be wrong, but what about ................. "
You say, "Yeah, I got a different answer. I think it might be..." Why do you couch it that way? Well, one reason is you might be wrong. You sound arrogant telling someone they're wrong because it arrogantly assumes that you're not wrong when sometimes you are. So phrase it in a way where you're then both figuring out which of you is right, if either of you are.