中学立体几何中，二面角的平面角计算既是立几学习中的重点又是难点，也是历年高考命题的热点．二面角的平面角的计算关键是作出平面角，由于作平面角融会了立几中的四个重要定理：三垂线定理及逆定理，面面垂直的判定定理和面面垂直的性质定理，且作平面角的方法多灵活性大， In the three-dimensional geometry of middle school, the calculation of the planar angle of the dihedral angle is not only the key point but also the difficulty in the learning process, and it is also the hot spot of the college entrance examination proposition. The key to calculating the plane angle of the dihedral angle is to make the plane angles. The four important theorems in the vertical planes are merged for the plane angles: the tri-vertical line theorem and the inverse theorem, the face surface vertical decision theorem, and the surface vertical property theorem. , And the method of making plane angles is more flexible.