函数单调性定义的结构中有三个内容:一是在函数定义域内某个区间上的两个值x1与x2的大小;二是函数值f(x1)与f(x2)的大小;三是函数在给定区间上的单调性.在这三个内容中如果知道两个,就可以确定另外一个.因此,函数单调性的定义有下列三种用法. The definition of function monotonicity has three elements in its structure: one is the size of two values ​​x1 and x2 over a certain interval in the function definition domain; the other is the size of the function values ​​f (x1) and f (x2); the third is the function Monotonicity in a given interval, the other one can be determined by knowing two of these three contents, so the definition of monotonicity has the following three usages.