Further Binomial Expansions (3 of 4: Sigma Notation)

From a channel Lumen includes in full: Eddie Woo, an Australian high-school maths teacher, records his actual classroom lessons across algebra, trigonometry, calculus and proof, explaining the ideas with energy and care.

A 6-minute video from Eddie Woo's catalogue; the title names its topic.

Video by Eddie Woo, played through YouTube's embedded player.