函数描述了自然界中量的依存关系，是对问题本身的数量特征和制约关系的一种刻画，所以函数思想的实质是到除问题的非数学特征，用联系与变化的观点提出数学对象，抽象其数量特征，建立函数关系．与这种思想相联系的就是方程的思想．如果变量间的数量关系用解析式表示，则这个 The function describes the dependence of quantity in the nature, which is a description of the quantitative characteristics and constraints of the problem itself. Therefore, the essence of the function idea is to remove the non-mathematical features of the problem, and to propose mathematical objects from the viewpoint of connection and change. Its quantitative characteristics establish functional relationships. Associated with this idea is the idea of ​​equations. If the quantitative relationship between variables is expressed in analytical terms, then this