"obvious how ..." vs "obvious of how ..."

Question

An example of "obvious how ..." from Definition of obvious adjective from the Oxford Advanced Learner's Dictionary:

• obvious how, what, etc.
  It was far from obvious how they were going to get off the island.

An example of "obvious of how ..." from a video of Khan Academy at around 3:00:

This is a one minus cosine squared theta, so it's not completely obvious yet of how you can simplify it, until you realize that this could be viewed as a difference of squares.

Question

• Is there any difference between "obvious how ..." and "obvious of how ..."?

Answer 1

"Obvious of how" is not correct. It may have been a slip of the tongue.