正弦定理和余弦定理是解斜三角形和判定三角形类型的重要工具,其主要作用是将已知条件中的边、角关系转化为角的关系或边的关系.现将正、余弦定理的三种用途加以说明.一、判断三角形的形状给出三角形中的三角关系式,判断此三角形的形状. The sine theorem and the cosine theorem are important tools for solving oblique triangles and determining the types of triangles. Their main role is to convert the relationship between edges and angles in known conditions to the relationship of angles or edges. Now we have three kinds of positive and cosine theorems. Uses to explain. First, determine the shape of the triangle gives the triangular relationship in the triangle, determine the shape of the triangle.