在圆锥曲线中经常会遇到直线与曲线相交的问题,解决的关键是利用联立方程组的方法,进而化简处理,但计算量较大.若条件与相交弦的中点有关,通常称其为中点弦,对中点弦问题有特殊的处理方法——点差法(或称设而不求法),下面举例说明. In the conic curve often encounter the intersection of the straight line and the curve, the key to solve the problem is to use simultaneous equations method, and then simplify the processing, but a large amount of computation .If the conditions and the intersection of chord midpoint, usually It is a mid-point string, and there is a special treatment for the mid-point string problem-the spread method (or set without seeking), as an example below.