You can refer to this website/view/c1aacfa0f524ccbf12184bc.html for the solution and evaluation of this problem. Summary: The distance formula from point to straight line can get the distance from P to straight line AB, and the key is how to find straight line AB. This is the midpoint chord problem in the elliptic problem. One conclusion (in the analysis, I couldn't type it out because I was stupid) was drawn by the difference method. Over time, your problem-solving ideas will become wider and wider! ! !