【摘要】 通过对《画法几何学》中直角投影定理的逆定理的研究,得出:“若垂直相交的两直线在某一投影面上投影成直角,则该两直线至少有一条直线平行于该投影面”的推论。此推论使得直角投影定理自身更趋于完整,同时,对垂直相交两直线的判断和作图也有一定帮助。更多还原

【Abstract】 This paper investigates the converse theorem of rectangular projection theorem in descriptive geometry,and furthermore supplements and confirms another converse theorem,"If the projection of two lines intersecting vertically fo’rms a rectangle on a certain projecting plane,at least one line of the two lines is parallel to the projecting plane. " This supplement to the theorem perfects the rectangular protection theorem,and helps judge two lines intersecting vertically and draw graphs.更多还原