众所周知,三次函数是多项式函数中相对比较简单的一类,而其导函数又是中学数学中非常常见的二次函数,因此,导函数的应用中关于三次函数的问题层出不穷。作者曾针对三次函数图像的切线问题进行了一些研究,其中一项结果表明,过三次函数图像的对称中心仅能作一条与三次函数图像相切的直线,而过三次函数图像上除对称中心之外的点可以作两条与三次函数图像相切的直线[1]。事实上,即使过三次函数图像外的某一点,仍然可以作出三次函数图像的切 It is well-known that cubic functions are relatively simple types of polynomial functions, and their derivative functions are very common quadratic functions in high school mathematics. Therefore, the problems concerning the cubic functions in the application of derivative functions emerge one after another. The author has done some researches on the tangential problem of the cubic function image. One of the results shows that the center of symmetry of a cubic function image can only be a straight line tangent to the cubic function image, The outer points can be two lines tangent to the cubic function image [1]. In fact, even after a certain point outside the function image three times, it is still possible to make a cubic function image cut