三、圆锥曲线的焦点弦问题过焦点的直线与圆锥曲线相交,两个交点的线段叫焦点弦,与焦点弦有关的圆锥曲线问题常用定义(特别是第二定义中的焦半径公式)把问题转化.1.如果弦MN过椭圆的焦点F1,设M(x1,y1),N(x2,y2),则|MN|=a+ex1+a+ex2=2a+e(x1+x2).【例6】设椭圆方程为ax22+by22=1 Third, the conical curve of the focus of the string problem over the focus of the line and the conic curve intersect, the two intersections of the line is called the focus of the chord, and the focus of the conical curve problem related to the commonly used definition (especially the second definition of the focal radius formula) to the problem Transformation 1. If the string MN crosses the ellipse’s focus F1, set M(x1,y1),N(x2,y2), then |MN|=a+ex1+a+ex2=2a+e(x1+x2). [Example 6] Let elliptic equation be ax22+by22=1