Circles

Page 1

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.

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.

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.

Page 2

Circumference = Pi x Diameter

Area = Pi x Radius squared

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.

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.

Page 3

Pi (π) Draw a circle with a radius of 1.

The distance half way around the circle

is 3.14159265... a number known as Pi

Pi (the symbol is the Greek letter π) is:

Or you could draw a circle with a diameter of 1.

Then the circumference (the distance

all the way around the circle) will be Pi

The ratio of the Circumference

to the Diameter

of a Circle.

To help you remember just draw this diagram.