圆是平面几何中的基本图形,看似朴实无华,实则魅力无穷.我们把顶点在圆上,且两边都和圆相交的角叫圆周角;圆外角指顶点在圆外,且两边都和圆相交的角;圆内角指顶点在圆内的角.这三种角之间有大小关系:一条弧所对的圆内角>它所对的圆周角>它所对的圆外角.如图1,圆周角∠C>圆外角∠D,这是因为∠C=∠AEB>∠D;图2中同理有圆周角∠C<圆内角∠ADB. Circle is the basic figure in the plane geometry, seemingly simple, but in fact the charm of infinite. We put the vertices on the circle, and both sides of the circle and the intersection of the circle is called the corner angle; circle outer corner refers to the vertex outside the circle, and both sides and the circle The angle of intersection of the circle; the angle of the circle refers to the angle of the vertex in the circle.The size of the relationship between these three angles: the angle of the circle to which an arc is located> the angle to which it circulates> the angle to which it circles. Circumferential angle ∠C> round angle ∠D, this is because ∠C = ∠AEB> ∠D; Similarly, in Figure 2, the circumferential angle ∠C