The straight line connecting the two ends of the arc is the "chord", which is the chord.

The area surrounded by chords and arcs is the "bow", that is, the line segment.

The area surrounded by an arc and two radii is a "sector", that is, a sector.

2. The arc larger than the semicircle is the "optimal arc" and the main arc; ;

An arc smaller than a semicircle is a "bad arc" and a small arc.

⌒

3.AB represents the arc length between A and B;

Add a straight line above ab to indicate the chord length between a and b,

It can also be expressed by absolute value coincidence degree, such as |AB|, which is modulus in English.

4.∩ indicates the same part of two sets, namely "intersection" and "intersection".

For example, a = {1, 2,3,4,5,6} and b = {22,4,6,8}.

A ∩ B = {2，4，6}