Identities with complex numbers

My apologies if this is in the wrong forum, please notify me and move if it is?

I'm currently learning pre-calculus on this site and and am on the unit "Identities with complex numbers". Now I've been succesful thus far on this site, but sadly, I am stuck on this part of the site (Identities with complex numbers), what has helped myself get through previous units is when videos AND notes have been posted to help with learning, and I was wondering, would anyone that is working for Khan Academy be able to post notes under this unit as well? That would be such a big help and I would be so grateful for the help please.