The formula editor in word can input all mathematical characters. The value of the boundary m is not compared with the value of x. It is compared with the absolute value of f(x). That is to say, the absolute value of the maximum value that f(x) can take in the domain of X is compared with the absolute value of the minimum value. For example, the sinx field is the entire real number axis. The range is (-1, 1). That is to say, the absolute value of f(x) is less than 1. At this time, m in the original formula can take any value greater than or equal to 1. Can be used as the boundary of sinx. That is, its minimum upper bound and maximum lower bound are 1 and-1 respectively. Values greater than 1 less than-1 can be regarded as the bounds of the function. It can also be understood that there are countless boundaries. But it is usually to find the maximum lower bound and the minimum upper bound