“直角三角形法”的实质——谈对“求一般位置直线的实长”教学的改进

The Nature of the Method of Right Triangle

作者根据其教学实践,认为对于“求一般位置直线的实长”教学,现有的教材和教学如能再深入一些,使学生懂得“直角三角形法”的实质——即空间直线具有长、宽、高三个尺度,它的每一面投影具有两个尺度,其空间实长=(长~2+宽~2+高~2)^(1/2) ,则会使学生更容易掌握求该实长的方法。

According to the writer' s teaching practice, he thinks that the present textbooks and teaching activities should be improved when teaching the students to evaluate the real length of a straight line in a general position,thus the students may easily know the nature of 'the method of right triangle'. The students will know that a straight line in space has three yardsticks<length, width and height> ,its projection has two yardsticks and the length in space equals,