Stands for subscript, that is to say, you can take the set of natural numbers of 1, 2, 3, 4, and n is generally infinite. If the topic specifically limits the scope, then n is limited. How many numbers are there in this column? N is called N mathematically, and an stands for the nth number. For example, a 1 means the first number, that is, 1. Similarly, a2=3, a3=5, and the number of the nth item is an.

normality

The curve is bell-shaped, with low ends, high middle and symmetrical left and right. Because it is a bell curve, people often call it a bell curve. If the random variable X obeys the normal distribution with a mathematical expectation of μ and a variance of σ2, it is recorded as N(μ, σ2). The expected value μ of probability density function with normal distribution determines its position, and its standard deviation σ determines its distribution amplitude. When μ = 0 and σ = 1, the normal distribution is standard normal distribution.