THE CIRCLE

Circle

A circle is a plane shape made by drawing a curve that is always the same distance from a centre. 

 

The Radius is the distance from the center to the edge.
The Diameter starts at one side of the circle, goes through the center and ends on the other side.
The Circumference is the distance around the edge of the circle.

Note that the Diameter is twice the Radius:

Diameter = 2 × Radius

Lines

A line that goes from one point to another on the circle's circumference is called a Chord.
If that line passes through the center it is called a Diameter.
A line that "just touches" the circle as it passes by is called a Tangent.
A line that intersects the circle is called intersecting or secant line.
And a part of the circumference is called an Arc.

 Slices

There are two main "slices" of a circle. The "pizza" slice is called a sector. And the slice made by a chord is called a segment.

Common Sectors

The Quadrant and Semicircle are two special types of Sector:

	Quarter of a circle is called a Quadrant.             Half a circle is called a Semicircle.