The arc of a semicircle is 180 degrees, and there is only one symmetrical line. Two endpoints of any diameter of a circle divide the circle into two arcs, and each arc is called a semicircle. The semicircle should be separated from the semicircle, because the semicircle is just an arc, which is half of a circle. The center of a semicircle is the center of its concentric circle, with only one diameter, but countless radii and an axis of symmetry.
Semicircle arithmetic
Semi-circle can construct the arithmetic and geometric mean of two lengths with a ruler and compasses, and make a semi-circle with a diameter of A plus B. Then the length of radius is the arithmetic mean of A and B. Since the radius is half of the diameter, the geometric mean can be obtained by dividing the diameter into two sections with lengths of A and B, and then connecting the same endpoint of * * to the semi-circle with a line segment perpendicular to the diameter.