本刊1978年第6期刊登的《怎样画大圆弧的放大图》一文,介绍了用计算法画大圓弧的方法。这里介绍一种根据同弧上的圆周角相等的逆定理制成的大圓弧的画规。在图1中,C点是AB的中点令∠ABC=2α AB=L,CE=H∵H=(L/2)ctgα根据弦高法测R的公式可列下式: 根据同弧上的圆周角相等的逆定理。可知只要满足∠ADB=∠ACB,则D点必定在AB上, The publication of No. 6, 1978, published in the “how to draw large arc enlargement” article, introduced the method of computing large arcs. Here is a description of a large arc based on the inverse theorem that the circumferential angles on the same arc are equal. In Figure 1, C is the midpoint of AB so that ABAB = 2αAB = L, CE = H∵H = (L / 2) ctgα The formula for R according to the chord height method can be expressed as follows: The inverse of the equal circumferential angle. We can see that as long as meet ∠ ADB = ∠ ACB, D point must be on AB,