∑ formula calculation: the number indicating the beginning and end. For example, i=2 below, and the number 10 above means from 2 to 10.
For example, 10∑(2i+ 1) represents the summation formula: (2 * 2+1)+(2 * 3+1)+...+(2).
In the formula i=2, 2i+ 1 is the general formula a i of the series, I is the ordinal number of the item, and i=2 means starting from the second item of the series {2i+ 1}, and the top 10 is the end of the calculation of the item 10.
2. The usage of ∑:
Where I stands for the lower bound, n stands for the upper bound, and k starts from I and goes all the way to n, all of which add up.
∑i can also be expressed as the sum of I, which is a variable.
Basic information
In mathematics, we use ∑ as the summation symbol; Use the lowercase letter σ to indicate the standard deviation.
In physics, we use its lowercase letter σ to represent the area density. (Accordingly, ρ stands for bulk density and η stands for linear density). Area density is the mass per unit area of materials with specific thickness in terms of engineering materials.
In chemistry, we use its lowercase letter σ to represent a valence bond. The valence bond formed by the overlapping of two atomic orbits along the direction of orbital symmetry axis increases the probability of electrons appearing between nuclei, which is called σ bond. σ bond is a localized bond, which can be a general valence bond or a coordination valence bond. Generally, single bonds are σ bonds.