在这些年来不断进行的教改中,人教版的数学教材也有了不少变化,特别是圆中的大量定理被删除,降低了初中阶段数学学习的难度,而保留的一些题目都是可以用三角形的相关知识解决的.然而,不难发现,借用与圆相关的知识可以使证明更加便利.请看如下模板:如图1,Rt△ABC和Rt△DBC中,∠BAC=90°,∠BCD=90°.求证:A、B、C、D四点共圆. In the continuous reform in these years, the PEP has changed quite a lot in math teaching materials. In particular, a large number of theorems in the circle have been deleted, which has reduced the difficulty of maths learning in junior high schools. Some of the topics reserved are triangles However, it is not difficult to find that borrowing circle-related knowledge can make the proof more convenient. Look at the following template: As shown in Figure 1, RtΔABC and RtΔDBC, ∠BAC = 90 °, ∠BCD = 90 °. Proof: A, B, C, D four points were round.