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Home » Articles » LESSON NOTES (Mathematics) » Upper Primary


LEARN FORMULAS FOR DIFFERENT POLYGONS: PART 2

CIRCLE

Learn some parts of a circle and formulae

 

Before we learn formulas for finding areas and circumference of circles, let’s discuss the following:

Consider the circle below:

 

Radius is a straight line from the center to any point on the circumference of a circle or sphere.

From the illustration above: the Radius is the line segment CO

 

Diameter: is a straight line joining two points on the circumference and passing through the centre.

From the illustration above: the Diameter is the line segment AB

 

Chord: is any straight line joining two points on the circumference.

From the illustration above: the Chord is the line segment DE

Note: A diameter is a chord passing through the centre.

 

A sector: is a portion of a circle enclosed by two radii.

From the illustration above: the Sector is the figure AOC

 

An arc: is a connected section of the circumference of a circle.

From the illustration above: the arcs are AC, CB, BE, ED and DA

 

A segment is a portion of a circle enclosed by a chord.

 

 

FORMULAE

 

Circle:

Area = πr2 which means (π x r x r)

Circumference = πD which means π x D

 

Semi Circle:

Area = 1/2 πr2 which means (1/2 x π x r x r)

Circumference = 1/2 πD + D

 

Three quarter circle

Area = 3/4 πr2 which means (3/4 x π x r x r)

Circumference = 3/4 πD + D

 

Quarter circle:

Area = 1/4 πr2 which means (1/4 x π x r x r)

Circumference = 1/4 πD + D

 

Sector:

Area = θ/360 πr2 which means ( θ/360 x π x r x r)

Circumference = θ/360 πD + D

 

Circle with given angle:

Area = θ/360 πr2 which means ( θ/360 x π x r x r)

Circumference = θ/360 πD + D

 

************* END ********************

Category: Upper Primary | Added by: Admin (07/Apr/2017) | Author: Yahya Mohamed (Badshah) E W
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