∑ English name is Sigma, Chinese name is Sigma (capital σ, lowercase σ), the18th Greek letter. In Greek, if the last letter of a word is lowercase sigma, what should it be written as? .

Capital σ is used for mathematical summation symbols, such as ∑Pi, where i= 1, 2, ..., t, which is the sum of P 1+P2+ and ...+angle. Lowercase σ is used for statistical standard deviation. Both the с of Cyrillic alphabet and the S of Latin alphabet are derived from Sigma.

The above explanation:

The commonly used methods in summation are formula method, dislocation subtraction, anti-addition, grouping method, split term method, mathematical induction method, general term reduction method and union term summation method. 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.

This is the method used to derive the sum formula of the first n terms of arithmetic progression, that is, to arrange a series in reverse order (reverse order) and then add it to the original series to get n (a 1+an), Sn? =a 1+ a2+ a3+......+an、Sn？ = an+an- 1+an-2+a 1，Sn=(a 1+an)n/2。