余弦定理的变着和活用江西省新干县第二职业技术中学谢春如余弦定理是揭示三角形边角关系的重要定理．直接应用它可解决已知三角形两边及夹角求第三边和已知三边求角的问题．若对余弦定理加以变形并适当地迁移于其它知识，应用更为广泛．一、掌握变式，巧用余弦定理余弦定... The change of the cosine theorem and the application of the cosine theorem of Xie Chunru, the second vocational technology school in Xingan County of Jiangxi Province, are the important theorems for revealing the relationship between triangle corners. Applying it directly solves the problem of finding the angle between the two sides of the known triangle and the angle between the third edge and the known three sides. If the cosine theorem is modified and properly migrated to other knowledge, it is more widely used. First, master the variants, use the cosine theorem cosine...