What is the summation formula of series? Sn=(a 1+an)n/2 (arithmetic), Sn=a 1( 1？ qn) 1？ Q (equal proportion).

The sum of series sums the numbers arranged according to a certain law. Finding Sn is essentially a general formula for finding Sn, so we should pay attention to understanding its meaning. Common methods include formula method, dislocation subtraction method, anti-addition method, grouping method, split term method, mathematical induction method, general term reduction method and union term summation method.

Sequence is an important content of algebra in senior high school, and it is also the basis of learning advanced mathematics. It plays an important role in college entrance examination and various math competitions. Sum of series is one of the important contents of series. Except arithmetic progression and geometric progression have summation formulas, the summation of most series requires certain skills.

Series:

Sequence is a function with positive integer set (or its finite set) as its domain, and it is an ordered number. Every number in a series is called an item in this series. The number ranked first is called 1 item of this series (usually also called the first item), the number ranked second is called the second item of this series, and so on, and the number ranked n is called the n item of this series, usually represented by an.

The famous series include Fibonacci series, trigonometric function, Cartland number, Yang Hui triangle and so on.

The items in the sequence must be numbers, which can be real numbers or complex numbers.

The symbol {an} is used to represent a series, which is just the symbol of "borrowing" the set. There is an essential difference between them: 1. The elements in the set are different from each other, but the items in the series can be the same. 2. The elements in the set are out of order, and the items in the series must be arranged in a certain order, that is to say, they must be orderly.