The second grade math semicircle has no corners. In mathematics (especially geometry), a semicircle is a one-dimensional trajectory of points forming a semicircle. The radian of a semicircle is always 180 (equivalent to π radian or half a circle). It has only one line of symmetry (reflection symmetry).

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. It is a half circle, and the center position of the half circle is the center position of its concentric circle. It has only one diameter, but it has countless radii and an axis of symmetry.