The vertex is on the circle, and the angle at which both sides intersect the circle is called the circumferential angle.
Inference 1 is equal to the circumferential angle of the same arc or equal arc; Equal circle in the same circle or equal circle.
The arcs subtended by these angles are also equal.
Inference 2: the circumference angle (or diameter) of a semicircle is a right angle; A 90-degree circumferential angle.
A chord is a diameter.
Inference 3 If the median line of one side of a triangle is equal to half of this side, then this triangle
This is a right triangle.