__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 = πr^{2 }which means (π x r x r)
Circumference = πD which means π x D
__Semi Circle:__
Area = ^{1}/_{2} πr^{2} which means (^{1}/_{2} x π x r x r)
Circumference = ^{1}/_{2} πD + D
__Three quarter circle__
Area = ^{3}/_{4} πr^{2} which means (^{3}/_{4} x π x r x r)
Circumference = ^{3}/_{4} πD + D
__Quarter circle:__
Area = ^{1}/_{4} πr^{2} which means (^{1}/_{4} x π x r x r)
Circumference = ^{1}/_{4} πD + D
__Sector:__
Area = ^{θ}/_{360 } πr^{2} which means ( ^{θ}/_{360 } x π x r x r)
Circumference = ^{θ}/_{360 } πD + D
__Circle with given angle:__
Area = ^{θ}/_{360 } πr^{2} which means ( ^{θ}/_{360 } x π x r x r)
Circumference = ^{θ}/_{360 } πD + D
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