σ is used for:
● Mathematical summation symbol (also called sum number)
● Sima in Locke X, the old enemy of X and zero.
Lowercase σ is used for:
Sigma bond, a chemical bond formed by the "head-to-head" of atomic orbits.
● Statistical standard deviation
The symbol "σ" was first used by Euler (1707- 1783) in 1755. This symbol comes from the Greek prefix (addition), and "σ" is the capital of σ.
For example: σ an = a 1+a2+...+ An
∑ is a simple symbol of summation of series, followed by k 2 is a general term formula, the following k= 1 is the number of terms at the beginning of the initial term, and the above n is the number of terms at the end.
n
∑k^2= 1^2+2^2+……+n^2( 1)
k= 1
n
∑(2k+ 1)= 3+5+……+(2n+ 1)(2)
k= 1
Then (1)+(2)= 1
n
∑(k+ 1)^2=2^2+3^2+……+(n+ 1)^2
k= 1
The extension of the famous binomial theorem can be expressed as
n
∑C(n,k)a^(n-k)b^k.
k=0
This shows the possibility of application, and its application is quite flexible.