Theory:

Circumference of the circle:
The circumference of the circle is defined as the pi(\(π\)) multiply with the diameter of the circle(\(d\)). The degree of the circle is 360°.
 
Circumference of the circle = \(\pi\times d\) units (where \(d=2\times r\)).
 
\(= \pi\times 2\times r=2\pi r\) units
 
Where π=3.14.
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Length of the arc of the semicircular quadrant:
The length of the arc of the semicircular quadrant is defined as the one by two(\(1/2\)) pi(\(π\)) multiply with the diameter of the circle(\(d\)). The degree of the semicircle is \(180°\).
 
Circumference of the circle = \(\pi\times d\) units (where \(d=2\times r\)).
 
\(= \pi\times 2\times r=2\pi r\) units
 
Length of semicircle arc (\(l\)) = \(\frac{1}{2}\times 2\pi r\) units.
 
It can also be written as 180°360°×2πr units (where the degree of semicircle is 180°).
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Length of the arc of the one third of the circle:
The length of the arc of the one-third of the circle is defined as the one by three(\(1/3\)) pi(\(π\)) multiply with the diameter of the circle(\(d\)). The degree of the one-third of the circle is \(120°\).
 
Circumference of the circle = \(\pi\times d\) units (where \(d=2\times r\)).
 
\(= \pi\times 2\times r=2\pi r\) units
 
Length of the one third of the circle arc = \(\frac{1}{3}\times 2 \pi r\) units.
 
It can also be written as 120°360°×2πr units (where the degree of one third of the circle is 120°).
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Length of the arc of the circular quadrant:
The length of the arc of the circular quadrant is defined as the one by four or quarter(\(1/4\)) pi(\(π\)) multiply with the diameter of the circle(\(d\)). The degree of the arc of the circular quadrant is \(90°\).
 
Circumference of the circle = \(\pi\times d\) units (where \(d=2\times r\)).
 
\(= \pi\times 2\times r=2\pi r\) units
 
Length of the quadrant arc(\(l\)) = \(\frac{1}{4}\times 2 \pi r\) units.
 
It can also be written as 90°360°×2πr units (where the degree of quadrant is 90°).
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From the above explanation, we get an idea that the length of the arc is equal to the pi(\(π\)) multiply with the diameter of the circle(\(d\)) by θ°360°
Therefore the length of the arc l=θ°360°×2πr.
Important!
If a circle of radius(\(r\)) units divided into \(n\) equal sectors, then the length of arc = \(\frac{1}{n}\times 2\pi r\) units.