39. The radius of a circle is the distance from the center of the circle to the outside edge. RADIUS
40. The diameter of a circle: The diameter of a circle is the longest distance across a circle. (The diameter cuts through the center of the circle. This is what makes it the longest distance.)
41. (the perimeter of a circle) The circumference of a circle is the perimeter -- the distance around the outer edge. Circumference = where r = the radius of the circle and pi = 3.141592...
42. A chord of a circle is a line segment that connects one point on the edge of the circle with another point on the circle. (The diameter is a chord -- it's just the longest chord!)
43. An arc of a circle is a segment of the circumference of the circle.
44. A sector of a circle is a pie shaped portion of the area of the circle. Technically, the piece of pie is between two segments coming out of the center of the circle.