I seem to have partially gotten this right, but am missing some answers, so chances are i stumbled across the (partial) right answer improperly. If someone could tell me what I'm doing wrong, that would be grand

on an interval of 0 - 2pi

using double angle identities and cotanget identity

multiply both sides by tanx

multiply both sides by

so that gives an answer at , but the book specifies additional answers at . Did I make a mistake above? If not, where are those 2 additional answers from?