For this problem, it is a difficult point in the senior high school entrance examination, and it is difficult to grasp it well. This is the first thing we should do to prepare psychologically. Derivation is a tool to study the correlation of function numbers, one is to study the tangent problem, the other is to study the interval problem of function numbers, and then to study the extreme value and maximum value when monotonicity is known. The classification theory we are talking about is after derivation (the definition domain of function number needs to be written first). It is necessary to study the value of derivative function when studying the three different situations of "positive, negative and zero" of derivative (that is, when the derivative is positive, negative and zero). But there are two kinds of functions that are different from linear and quadratic, so we must first determine whether it is linear or quadratic ~ that is, whether the initial parameter will be 0, which will lead to its degradation. The second time is that the initial parameters are positive or negative and the derivative function is positive or negative, the third time is to consider the existence of the roots of the quadratic form that is most often tested (that is, whether the discriminant will be less than or equal to 0, the number of derivative functions will always be non-negative or non-positive, and finally the number of original functions will always be monotonous), and the fourth time is to find two unequal roots of the quadratic form and consider their relationship. Finally, we need to consider the relationship between the extreme point and the end point given in the problem (sometimes the relationship between the end point and the extreme point of the definition domain). Generally, these five steps need to be considered, and the sequence is also given before. I did well in math in high school, but I can't work out this problem. Later, I asked the old teacher of Beijing New Oriental Youneng, and he said the same thing. I hope my answer can help you.