Parts of A Circle

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A circle is a curve on which every point is the same distance from the centre. This distance is called its radius.

The circumference is the measure of the distance around the circle.

NOTE: The names of some parts of a circle are used interchangeably with their measure. The radius could be the distance from the centre to the circumference or it could be the line joining the centre to the circle.

Parts of A Circle

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A diameter is an interval joining 2 opposite points on a circle. It passes through the centre.

A diameter is an axis of symmetry of the circle

NOTE: Some parts of a circle are used interchangeably with their measure. The diameter could be the distance from one point on the circumference to an opposite point or it could be the line through the centre of the circle.

More Parts of A Circle

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Semicircle: Half of a circle.

Note: Strictly speaking, a circle is a curve, so the yellow area is contained by the semicircle and the diameter. It is not part of the circle!

Diameter: The interval joining two opposite points on a circle.

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The diameter passes through the centre of the circle.

More Parts of A Circle

Chord: An interval joining any 2 points on a circle.

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A chord divides a circle into two segments.

Even More Parts of A Circle

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A chord divides a circle into two segments.

Major Segment

Minor Segment

A major segment …

… and a minor segment.

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Two radii divide a circle into two sectors.

Minor Sector Major

Sector

A major sector …

… and a minor sector.

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Even More Parts of A Circle

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Other Parts of A Circle

CIrcle Sectors

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A quadrant is a quarter of a circle.

It has an angle of 90º at the centre.

An arc is a part of the circumference of a circle.

A Tangent To A Circle

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Generally, a line will cut a circle in two places.

If the line is moved to the edge of the circle, the two points come together.

A tangent touches a circle in just one point.