初中数学在讲五等分圆周时,只讲了作法,未加证明。为使教者心中有底,现介绍五种证法以供参考。为了叙述的方便,将五等分圆周的尺规作图法择抄如下: 如图一,在单位圆内: 1.作两直径AB⊥CD,并取OC中点E。 2.以E为圆心,EA为半径作弧交OD于F。 3.连AF,则AF即为⊙O内接正五边 When junior middle school mathematics talked about the quintile, it only talked about the practice and did not prove it. In order to make the teacher have a bottom in mind, five kinds of evidence are introduced for reference. For the sake of narrative convenience, the five-divided circumferential ruler drawing method will be selected and copied as follows: As shown in Figure 1, in the unit circle: 1. Make two diameters AB⊥CD, and take the OC midpoint E. 2. With E as the center, the EA is arced for OD to F. 3. Even AF, AF is ⊙O inward five sides