A sector is a part of the circle

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Perimeter of sector will be the distance around it

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Thus,

  Perimeter of sector = πœƒr + 2r

   = r(πœƒ + 2)

Where πœƒ is in radians

 

If angle is in degrees,

πœƒ = Angle × π/(180°)

 

Let us take some examples:

 

Find perimeter of sector whose radius is 2 cm and angle is of 90° 

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First,

We need to convert angle in radians

πœƒ = Angle in degree × π/(180°)

πœƒ = 90° × π/(180° )

πœƒ = π/4

 

And Radius = r

            = 2 cm

 

Now,

  Perimeter of sector  = r (πœƒ + 2)

    = 2 (π/4+2)

    = 2 ((π + 2 × 4)/4)

    = 2 ((π + 8)/4)

    = (π + 8)/4 cm

 

Find perimeter of sector whose radius is 2 cm and angle is π/4 radians

37.jpg

Radius = r

     = 2 cm

 

Angle (in radians) = πœƒ

      = π/4

Now,

  Perimeter of sector = r (πœƒ + 2)

  = 2 (π/4+2)

  = 2 ((π + 2 × 4)/4)= 2 ((π + 8)/4) = (π + 8)/4 cm

 

  1. Chapter 11 Class 7 Perimeter and Area
  2. Concept wise

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Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.