题目已知正方体 ABCD—A′B′C′D′的棱长为口,E、F 分别是棱 D′C′与 AB 的中点,求点 B 到截面 A′ECF 的距离.解法1 定义法定义法的关键是作出点到平面的垂线段.一般是通过已知点构造一个平面垂直于已知平面,再过已知点作两平面交线的垂线. The length of the known cube ABCD-A’B’C’D’ is the mouth, E and F are the midpoints of the edges D’C’ and AB respectively, and the distance from point B to the section A’ECF is determined. Solution 1 Definition The key point of the law definition method is to make a vertical line from the point to the plane. Generally, a vertical line perpendicular to the known plane and a known point as the intersection line of the two planes are constructed by known points.