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本文是圆锥与圆柱正交时,相贯线上难求的特殊点的投影求解方法。在“画法几何学”中,求两相交曲面立体相贯线的投影,首先要求出相贯线上特殊点的投影,对于圆锥与圆柱正交时,由于相贯线上特殊点有的难求,在目前国内出版的教材中,对难求的特点就不求找了,有的教材甚致是用错误的方法来求找。所以教师讲解此处内容,总是感到困难。近几年国内有些同志对此问题作了专门的研究。有的同志用图算结合的方法来求找,有的同志用作图法来求解。但是,要说明这些方法的正确性,需要进行复杂的数学推导来证明,给学生讲解起来很麻烦,并且课时也不允许。本文是采取学生所掌握的科学知识,用几句话就能讲清求解出相贯线上难求的特殊点的方法。
This paper is a projection method to solve the special point which is hard to find on the intersecting line when the cone and the cylinder are orthogonal. In “Geometry of Painting”, we need to find the projection of the special points on the intersecting lines for the projection of the three-dimensional intersecting lines of the intersecting surfaces. When the conic and the column are orthogonal, due to the special points on the intersecting lines Seeking, in the current domestic teaching materials, the characteristics of hard to find do not look for, and some teaching materials is very wrong way to find. Therefore, the teacher to explain the content here, always feel difficult. In recent years, some comrades in our country have made special studies on this issue. Some comrades use the method of calculation to find the way, and some comrades use it as a solution to the problem. However, to prove the correctness of these methods, complicated mathematical derivation is required to prove that it is troublesome to explain to students and that class hours are not allowed. This article is to take students to master the scientific knowledge, with a few words will be able to clarify the intersection of the line difficult to find a special way.