在研究直线被圆锥曲线截得中点弦问题时,常设出弦端点坐标,并代入圆锥曲线方程得两式,将两式相减.这种解题方法,不妨叫设点求差法,简称点差法,其解题的主要步骤有:1.设弦的端点坐标;2.代入方程两式相减;3.建立端点与中点的坐标关系;4.求弦所在直线斜率.点差法解题过程规律化,运算简单化,适 In the study of the straight line by the conic section of the midpoint of the chord problem, the standing end of the string coordinates of the end of the line, and into the conic equation two equations, the two subtraction .This problem-solving method, may wish to set the point difference method, referred to as Spread point method, the main steps to solve the problem are: 1. Set the coordinates of the end of the string; 2. Substitute two equations subtraction; 3. Set up the coordinates of the end point and the middle point; Problem of the process of law, simplistic operation, suitable