Åk 6–9
 
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3.5 Circle
There are a number of concepts connected to circles.  It is a good idea to know them.




Center
This point is exactly in the middle of the circle.





Radius
A line from the center point to a point on the circle’s arc.

The segment is abbreviated r and is the same as half the diameter.




Cord
A segment between two points on the circle.

A cord does not have to go through the center point.





Diameter
A segment between two points on a circle which goes through the center point.

Can be abbreviated d.





Circle Arc
A continuous length of a part of the circle’s circumference.





Circular segment
An area which is limited by a circle’s arc and a cord between the arc’s endpoints.





Circle Sector
An area which is which is limited by a circle’s arc and radiuses to the arcs end points.

Area = p · r2 ·
v
360





The Circle’s Area and Circumference

The Circle’s Area
Can be defined as the measure of the surface within the circle’s arc.
Area =
p · r2

The Circle’s Circumference
Can be defined as the measure of the circle’s arc.
Circumference =
p · 2r = p · d





Inscribed circle

Circumscribed circle