九年级《数学》教科书中,给出了圆心角、圆周角的概念和性质,其实圆中还有圆外角和圆内角.一、圆外角顶点在圆外,并且两边都和圆相交(或相切)的角叫做圆外角.如图1-1,图1-2,图1-3三个图中的∠APB都是圆外角.圆外角的度数在数值上等于它所夹的两条弧线的度数差(较大弧的度数减去较小弧的度 In ninth grade mathematics textbook, given the concept of central angle and circumferential angle of the nature, in fact, there are round outside the circle and inside the circle. First, the outside corner of the circle outside the circle, and both sides and the circle intersect (or phase Cut) angle is called the circle outside the angle.As shown in Figure 1-1, Figure 1-2, Figure 1-3 three 的APB are round outer corner.The angle of the outer circle is equal to the numerical value of the two arcs The difference between the lines (the degree of the larger arc minus the degree of the smaller arc