This interplay of action and reaction as the independent variable moves closer to a given value is the essence of the idea of a limit. Limits provide the means of defining the derivative and integral of a function.

• 独立变量越来越接近一个给定的值的这种作用与反作用的相互作用是极限概念的基本点。极限提供了定义函数的导数和积分的方法。