

Radius  The radius is the distance from the center point to the edge of the circle. This is the same distance R we used to make the circle in our definition. 
Diameter  The diameter is a straight line that goes across the circle and through the center. It's twice the length of the radius. This gives you our first math equation for the circle: 
Circumference  The circumference is the distance around the circle. We use the following formula to figure the circumference:
c = d * π 
Sector  A sector is a section of the circle made by two different radii. Sort of like a piece of pizza or pie.
Chord  A chord is a line segment that joins two points on the circle. The diameter is a special type of chord that goes through the center point of the circle. 
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