18-25. True Or False
18. The diameter of a circle is trice the length of the radius.
19. A central angle is an angle formed by two radii.
20. A chord is a line segment joining two points on a circle called a diameter.
21. A circle is the set of all points in a plane with same distance from a certain point.
22. A radius is one-half of a diameter.
23. A circumference is a line segment around the circle.
24. A line segment that passes through the center of the circle is called a diameter.
25. A circle is a polygon.​