A circle is a simple closed curve which is not a polygon. We see
many things that are round, a clock, a bangle, coin.
Parts of a circle
Here is a circle with center C.
A, P, B, M are points on the circle.
Example: From the figure, identify:
a) The center of circle
b) Three radii
c) A diameter
d) A chord
e) Two points in the interior
f) A point in the exterior
g) A sector
h) A segment
a) O is the center of the circle.
b) OA, OB and OC are the three radii
c) AC is the diameter of the circle
d) ED is a chord
e) O and P are the two points in the interior.
f) Q is the point in the exterior
g) OAB (shaded portion) is a sector
h) ED (shaded portion) is a segment
Example: Say true or false:
a) Two diameters of a circle will necessarily intersect.
b) The center of a circle is always in its interior.
a) The two diameters of the circle will always intersect at the
b) True, the center of a circle will always lie in its interior.
a) Is every diameter of a circle also a chord?
b) Is every chord of a circle also a diameter?
a) Yes, every diameter of a circle is a chord. A chord is the line
segment joining any two points on the circle. Diameter is the
longest possible chord of the circle.
b) No, every chord is not a diameter because a diameter always
passes through the center, having its end points on the circle
whereas a chord may not necessarily pass through the center.