促使我思考“抛物线的定长弦中点横坐标的最小值”这个问题是在教学中遇到了下面一道题 :定长为 5的线段ＡＢ的两端点在抛物线ｙ2 =4ｘ上移动 ,设线段ＡＢ的中点为Ｍ ,求点Ｍ到准线的最短距离 .为该题提供的参考答案是这样解的 :把弦ＡＢ分成两类 :(1 )弦ＡＢ过焦点Ｆ时 ,过Ａ The problem that prompted me to think about the “minimum value of the abscissa at the midpoint of a parabola-fixed-length string” is that I encountered the following question in my teaching: Lines AB at a fixed length of 5 move at parabolic line y2 = 4x and line AB The midpoint is M. Find the shortest distance from the point M to the guideline. The answer to the question given in this question is solved as follows: Split the string AB into two categories: (1) When the string AB crosses the focus F, pass A