新编全日制十年制学校高中课本《数学》第四册,在“导数和微分的应用”一章中,介绍了“求闭区间[a,b]上的可导函数 f(x)在[a,b]上的最大值与最小值”的方法。此时函数 f(x)在[a,b]上连续,必有最大值与最小值存在。对于定义在非闭有限区间(a,b),[a,b),(a,b] In the fourth volume of the mathematics textbook for the new high school full-year 10-year school textbook, in the chapter “Application of derivatives and differentials”, the derivative function f(x) on the “closed interval [a,b]” The method of “maximum and minimum value on [a, b]”. At this point the function f(x) is continuous on [a,b] and there must be a maximum and a minimum. For definition in the non-closed finite interval (a,b), [a,b),(a,b)