高一立体几何教材中有一定理:斜线和平面所成的角,是这条斜线和平面内经过斜足的直线所成的一切角中最小的角(本文简称为最小角定理),教科书上对此定理的应用所配备的练习题很少,在立体几何关于研究角的不等关系的题目中,用此定理解决问题的方法也少见, There is a theorem in the high-a-dimensional geometry textbook: the angle formed by the slash and the plane is the smallest angle among all the angles formed by this oblique line and a straight line passing through a diagonal foot (herein referred to as the minimum angle theorem). Textbook There are very few exercises on the application of this theorem. In the problem of the unequal relations of the three-dimensional geometry with respect to the research angle, it is rare to use this theorem to solve the problem.