In this video we do an example of using the formal definition of a limit for an epsilon-delta proof of the limit of a quadratic function. There's one tricky part where we assume that delta = 1. After making the assumption we find an upper bound on an expression and work from there. Setting delta equal to 1 is a very common thing to do!

This is not a topic that you need to worry about for the AP Calculus AB or AP Calculus BC exam (definitely true in 2020...and since maybe the 1980s).