Who are you? Who am I? Where did we come from, and where are we going? Could I eat an entire pizza by myself? These are all questions about our identity. Some of them are easier to answer than others. The easy answers may lead to intestinal distress, though.
The identities we're really interested in today are the trig identities. We want more tricks for working with trig functions, and the double-angle and half-angle identities fit the bill. The addition formulas continue to be our MVFs (Most Valuable Formulas).