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A quick tutorial about circles to help you understand about calculating the area and circumference.

Try the Online Circle Measurement Tool.
If you know either the Diameter, Area or Circumference, the tool does the rest!


Lines in Circles

AB = Diameter
Must pass through the centre of the circle. The Diameter is equal to twice the radius.
OC = Radius
The radius is a line segment that begin from the centre and touches any point on the circle.
ED = Chord
The chord joins any two points on a circle.
FG = Tangent
A line with one point common to the circle.
EHD = Arc
Only the portion of the circle that is between two points on the circle.
ADB = Semicircle
Also considered to be an arc that is exactly half of the circle.
OCB = Sector
The area between two radii and the arc.
COB = Central Angle
Fromed by two radii.

The circumference of a circle is the actual length around the circle which is equal to 360°. Pi (p) is the number needed to compute the circumference of the circle.
p is equal to 3.14.
Pi is greek and has been around for over 2000 years!

In circles the AREA is equal to 3.14 (p) times the radius (r) to the power of 2.
Thus the formula looks like:
A= pr2.

In circles the circumference is 3.14 (p) times the Diameter.
Thus the formula looks like:
2pr or pd.

Related Links:
Measurement of area and perimeter of other shapes.
Geometry Tutorials


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