X obeys the distribution of n (u, σ 2) and is a normal distribution; Then the normal distribution in which z = (x-u)/σ obeys N(0, 1) is called standard normal distribution (that is, μ=0, σ= 1), which is the definition of mathematics. The standard normal distribution is the most widely used, and the appendix normal distribution table of the textbook is also checked. It is difficult to type out the formula of the derivation process.

μ is the mathematical expectation or population mean of the normal distribution curve,

O is the standard deviation of the normal distribution curve.