学习立体几何对培养同学们的逻辑思维能力和空间想象力有着不可替代的作用.然而在学习过程中,包括笔者在内的很多同学对二面角的平面角概念有些模糊,除了二面角的平面角唯一性之外,最值性也是它被用来度量二面角的重要原因.本文将使用数形结合的方法探讨二面角的平面角的最值性.我们在已知二面角的棱上取一点,过这一点在两个半平面上各引一条射线,它们的夹角 Learning three-dimensional geometry has an irreplaceable effect on cultivating students’ logical thinking ability and spatial imagination.However, during the learning process, many students, including the author, have some ambiguities about the concept of dihedral angle of plane angle, except for the dihedral In addition to the plane angle uniqueness, the most significant is also the important reason why it is used to measure the dihedral angle.This paper will discuss the maximum value of the dihedral angle by using the method of number-shape combination.In this paper, Take a point on the edge, over this point in the two half-planes each lead a ray, their angle