巧用单调性求最值蒲红军（宁夏固原民族师范７５６０００）在高中课本中有这样一道题：求函数ｙ＝ｘ＋３＋１ｘ＋３的最值．许多学生利用Ａ２＋１Ａ２２直接得到最小值２，这结论显然是错误的．因为只有Ａ＝１Ａ时Ａ２＋１Ａ２才能取最小值２，但在本题中ｘ＋３与１ｘ＋... Using monotonicity to find the best value Pu Hongjun (Ningxia Guyuan National Normal University 756000) has such a question in high school textbooks: find the function y=x+3+1x+3 the most value. Many students use A2+1A22 to directly obtain the minimum value of 2, which is obviously wrong. Because A2 + 1A2 can only take a minimum of 2 when A = 1A, but in this question x + 3 and 1x + ...