一、逆向思维的教学运用工程制图是以图示物,必须十分准确,不许有二义性。因此,在工程制图的准备知识正投影方法的学习中,投影的唯一性构成了正投影理论的原则。这一原则是教师要特别强调,学生要首先理解和铭记的。在投影作图练习中,怎样正确审题,把握住足够的已知条件,求出唯一的未知投影,是解题的关键和前提。在引导学生建立这一思维体系时,笔者 First, the use of reverse thinking teaching Drafting is based on the map object, must be very accurate, not allowed to have ambiguity. Therefore, the uniqueness of projection constitutes the principle of orthographic projection in the study of the orthographic projection method of engineering drawing preparation knowledge. This principle is particularly stressed by teachers, students should first understand and bear in mind. In the practice of projection mapping, how to correct the questions, grasp enough known conditions, and find the only unknown projection is the key and prerequisite for problem solving. In guiding students to establish this system of thinking, the author