几何图形按一定条件运动,有的几何量随着运动的变化而有规律变化,这就出现了轨迹和极值问题,而有的量却始终保持不变,这就是定值问题.解答动态几何定值问题的方法,一般有两种:第一种是先探求定值.再证明它能成立.探求的方法,常用特殊位置定值法,即把动点放在特殊的位置,找出定值的表达式, Geometric geometry according to certain conditions of movement, and some geometry with the movement of the changes in the law, which appeared trajectory and extreme value problems, and some have remained the same, and this is the problem of fixed value. There are two general methods of valuation problems: the first one is to explore the fixed value, and then prove that it can be established. The method of seeking, often using special position fixed value method, put the moving point in a special position to find out The value of the expression,