空间几何体是由点、线、面构成的,在处理立体几何问题时,巧用平面几何性质,可使问题简洁求解.本文利用三点共线原理,探究一类立体几何最值问题.题根平面四边形ABCD中,在对角线AC上寻找一点P,使其到点B、D距离之和最小.利用三点共线原理易知BD与AC的交点,即为所求的点P.下面就此性质的应用,进行变式探究. Spatial geometry consists of points, lines, and planes. When dealing with solid geometry problems, the use of planar geometric properties allows the problem to be solved in a simple way. This paper uses a three-point collinear principle to explore a class of three-dimensional geometrical value problems. In the planar quadrilateral ABCD, look for a point P on the diagonal AC to minimize the sum of the distances to points B and D. Using the three-point collinear principle, it is easy to know the intersection of BD and AC, which is the required point P. In this nature of the application, conduct variable exploration.