Sequences & Series

A sequence is an ordered list of numbers; a series is what you get when you add them up. This standard (AS91258) is about the two families that follow a rule: arithmetic (add the same amount each step) and geometric (multiply by the same amount each step). You find any term with a general-term formula, add many terms with a sum formula, and — for a shrinking geometric series — even add infinitely many terms to a finite total. Higher marks come from working backwards (finding the first term, common difference/ratio, or number of terms) and modelling real situations.