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一、二阶导数的定义原函数f(x)导一次叫一阶导数,那么把一阶导数f′(x)当做是新的一个函数再次求导,再导一次叫原函数f(x)二阶导数f″(x).二、二次求导的原因1.求导一次不能解答求零点问题(确定不了零点、正负性);2.我们通常在做求导问题的时候目的只是为了知道函数的单调性,因此我们只要关注导数的正负性即可,但是当需要判定函数的单调性而求导之后不能直接判定导数的符号时,可以考虑求二次导数.
The definition of the first and second derivatives The original function f(x) leads to the first derivative, then the first derivative f′(x) is regarded as a new function again. The derivative is called the original function f(x). Second derivatives f′′(x). Reasons for the second and second derivatives 1. The derivative cannot solve the zero-finding problem (cannot determine the zero point and the positive and negative); 2. We usually do the derivative problem when the purpose is only In order to know the monotonicity of the function, we only need to pay attention to the positive and negative of the derivative. However, when we need to determine the monotonicity of the function and then cannot determine the sign of the derivative directly, we can consider the second derivative.