I faced the following situation a few days back. I am doing my teaching assistance work under a professor.
I attended one of his classes as a TA during which he was teaching some technically wrong stuff, which he assumed as true. Since most of the class were students of the course, they do not know which statements are correct and hence are not in position to rectify the professor's mistakes.
There are more than five other TAs but no one pointed out the problem. I don't know whether the TAs know what is correct.
I stayed silent and observed whether anyone would point out the mistake but the class ended without anyone realizing the professor's mistake. The reason for my silence is this question.
Is it offensive to the professor to point out such mistakes? My question boils down to: Is it proper etiquette to point out mistakes that a professor makes during their lecture?