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MATHEMATICS;SECTORS AND SEDMENTS,PRELUDE TO CORCLE GEOMETRY

SEGMENTS AND SECTORS 

Slices

There are two main "slices" of a circle:

  • The "pizza" slice is called a Sector.
  • And the Segment, which is cut from the circle by a "chord" (a line between two points on the circle).

Try Them!

SectorSegment

Common Sectors

The Quadrant and Semicircle are two special types of Sector:

semicircle
Half a circle is
Semicircle.

quadrant
Quarter of a circle is
Quadrant.

Area of a Sector

You can work out the Area of a Sector by comparing its angle to the angle of a full circle.

Note: we are using radians for the angles.

circular sector area

This is the reasoning:

A circle has an angle of 2Ï€ and an Area of:Ï€r2
A Sector has an angle of Î¸ instead of 2Ï€ so its Area is :θ2Ï€ × Ï€r2
Which can be simplified to:θ2 × r2

 

Area of Sector = Î¸2 × r2   (when θ is in radians)

Area of Sector = Î¸ נπ360 × r2   (when θ is in degrees)

circular segment area

Area of Segment

The Area of a Segment is the area of a sector minus the triangular piece (shown in light blue here).

There is a lengthy reason, but the result is a slight modification of the Sector formula:

Area of Segment = Î¸ − sin(θ)2 × r2   (when θ is in radians)

Area of Segment = ( Î¸ נπ360 − sin(θ)) × r2   (when θ is in degrees)

 

circular sector arc length

Arc Length

The arc length (of a Sector or Segment) is:

L = θ × r   (when θ is in radians)

L = θ נπ180 × r   (when θ is in degrees)

 

 

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