Geometric series refers to a series in which the ratio of each term to its previous term is equal to the same constant from the second term, usually expressed by G and P. This constant is called the common ratio of geometric series, usually expressed by the letter Q (q≠0), and geometric series a 1≠ 0. Where each item in {an} is not 0. Note: When q= 1, an is a constant series.
formula
(1) Definition:
(2) General term formula (the general term formula of geometric series is derived from defined multiplication):
(3) Sum formula
Definition of proportional terms: Starting from the second term, every term (except the last term with finite series) is an item whose previous term is proportional to its subsequent term.
The most basic property: if m, n, p, q∈N+, m+n=p+q, then am×an=ap×aq.
The common ratio of 3 is the most important information given in the title of geometric series, so when seeking the answer to the title, we must pay attention to the information given in the title.