一、直接利用三角形或四边形内角和定理或推论求解．例1如图1，求的和．解，二、将多边形的角度计算问题转化为三角形或四边形问题，利用三角形或四边形内角和定理或推论求解．例2已知封闭折线ADGCFBEA，如图2，求的度数．解连结BG、DE．又例3延长四边形ABCD的对边AB、DC相交于 1. Solve directly using triangle or quadrilateral internal angles and theorem or inference. Example 1 is shown in Figure 1. Solution. 2. Convert the angle calculation problem of a polygon to a triangle or quadrilateral problem. Solve the problem by using triangles or quadrilateral internal angles and theorem or inference. Example 2 is known to seal the polyline ADGCFBEA, as shown in Figure 2, the number of degrees. Unlink the BG, DE. Also in Example 3, the opposite sides AB and DC of the extended quadrilateral ABCD intersect with each other.