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本文提出高中立体几何中课本中关于“斜线与平面所成的角,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.”的命题,作为最小角定理.并举例说明运用定理证明某些命题可以化繁为简、化难为易.
This paper proposes that the “angle formed by the diagonal line and the plane is the smallest angle among all the angles formed by this diagonal line and the line passing through the diagonal foot in the plane” in the textbook of the high school solid geometry, as the minimum angle theorem. In addition, examples are given to illustrate the use of theorem to prove that certain propositions can be simplified and simplified.