阅读了1999年第5期《建筑工人》刊登的《相似三角形性质在直线定线中的应用》一文后,觉得在运用相似三角形性质的同时,用三角形正弦定理和平行线性质,也能定出 C 点(图1中 AC′、C′D 为分析辅助线)。具体步骤如下:1.～4.与原文介绍的步骡相同;s.利用盘左、盘右观测∠α,即∠B′C′A; After reading the article “The Application of Similar Triangle Properties in Linear Alignment,” published by Construction Workers in No. 5, 1999, I feel that using the same trigonometric theorem and the properties of parallel lines, Point C (AC ’in Figure 1, C’D for the analysis of auxiliary lines). The specific steps are as follows: 1. ~ 4. The same as the introduction of the original step Mule; s. Use disk left, disk right observation ∠ α, that ∠ B’C’A;