一、引例例1(龙岩市一级达标校联盟2013年高三联考数学卷理科第8题)在同一平面内,下列说法:①若动点P到两个定点A、B的距离之和是定值,则点P的轨迹是椭圆;②若动点P到两个定点A、B的距离之差的绝对值是定值,则点P的轨迹是双曲线;③若动点P到定点A的距离等于P到定直线的距离,则点P的轨迹是抛物线;④若动点P到两个定点A、B的距离之比为定 First, cited Example 1 (Longyan a standard school union 2013 senior high school entrance examination mathematics and science subjects 8) in the same plane, the following statement: ① If the moving point P to the two fixed-point A, B and the distance is If the absolute value of the difference between the moving point P and the two fixed points A and B is a fixed value, then the trajectory of the point P is a hyperbola. If the moving point P reaches the fixed point A is equal to the distance P from a straight line, then the trajectory of the point P is a parabola; ④ If the moving point P to two fixed point A, B distance ratio is fixed