竞赛中,常出现求角的大小的题目.在这类题中,常涉及以下三种基本图形,为说话方便,分别命名为“M形”、“人字形”和“8字形”.这三种基本图形都有一个简单易记的性质.(请同学们证明).本文举例说明利用这三个性质解竞赛中的求解问题,供参考. In the competition, the title of the size of the angle is often seen. In such questions, the following three basic figures are often involved. For the convenience of speaking, they are named “M-shaped,” “herringbone,” and “8-character.” The basic graphics have a simple and easy-to-remember nature (please prove to the students). This article illustrates the use of these three properties to solve the problem of solving the contest for reference.