这是一个结构整齐、对称、富于数学美的公式.当且仅当λ>0(或λ<0且λ≠-1)时,分点位于P_1、P_2之间(或之外).当λ≠-1时,或者分点位于(或)延长线的无穷远处,”或者退缩为一点.这两种情形下,分点都不确定,其轨迹为一条直线.利用定比分点坐标公式,并注意以上对λ的讨论,能够推导出较多有用的结论,可简捷地解决较多数学问题. This is a formula that is neat, symmetrical, and full of mathematical beauty. If and only if λ>0 (or λ<0 and λ≠-1), the points are located between (or outside) P_1 and P_2. When ≠-1, or the sub-point is located at (or) at the infinity of the extension line, "or retreat to a point. In both cases, the sub-point is undefined, and its trajectory is a straight line. Using the coordinate formula of the fixed-score point, And pay attention to the above discussion of λ, can derive more useful conclusions, can easily solve more mathematical problems.