For a circle with radius r

 

Area of circle will be

  Area of circle = πœ‹ r 2

 

Here,

  πœ‹  can be taken as

  πœ‹ = 3.14 or πœ‹ = 22/7

 

Let’s take some examples

38.jpg

 

Find area of circle of radius 2 cm by counting squares , and also by formula

Area of circle - Part 2

 

Covered Area

Number

Area

1

Fully - filled squares

4

1 × 4 = 4

2

Half - filled squares

0

1/2 × 0 = 0

3

More than Half - filled squares

8

1 × 8 = 8

4

Less than Half - filled squares

4

0 × 4 = 0

Area of circle - Part 3

Area = 4 + 0 + 8 + 0

 = 12 cm 2

By formula of area of circle

Area = πœ‹r 2

 = 3.14 × (2) 2

 = 3.14 × 4

 = 314/100 × 4

         = 1256/100

         = 12.56 cm 2

Area of circle - Part 4

So, finding area by formula is more accurate

 

Find area of a circle with radius of 3.5 cm

Area of circle - Part 5

Radius = r = 3.5 m

 

Area = πœ‹r 2

= πœ‹ (3.5) 2

= 22/7 × (35/10) 2

= 22/7 × (7/2) 2

= 22/7 × 7/2 × 7/2

= 11/7 × 7/1 × 7/2

= 11/1 × 1 × 7/2

= 77/2

= 38.5 cm 2

∴ Area is 38.5 cm 2

 

Find area of a circle whose radius of 7 cm

Area of circle - Part 6

Radius = r = 7 cm

  Area = πœ‹ r 2

  = 22/7 × (7) 2

  = 22/7 × 7 × 7

  = 22 × 7

  = 154 cm 2

 

Area of circle - Part 7

 ∴ Area is 154 cm 2

 

Find area of a circle with diameter 21 cm

Area of circle - Part 8

Diameter = 21 cm

Radius = r = Diameter/2

    = 21/2 cm

Now,

  Area = πœ‹ r 2

          = 22/7 × (21/2) 2

          = 22/7 × 21/2 × 21/2

   = 11/7 × 21/1 × 21/2

   = 11/1 × 3 × 21/2

   = (33 × 21)/2

   = 693/2

           = 346.5 cm 2

Area of circle - Part 9

∴ Area is 346.5 cm 2

 

Find area of a circle with diameter 42 cm

Area of circle - Part 10

Diameter = 42 cm

Radius = r = Diameter/2

= 42/2 cm

= 21 cm

 

Now,

  Area = πœ‹ r 2

= 22/7 × (21) 2

= 22/7 × 21 × 21

= 22/1 × 3 × 21

= 66 × 21

= 1386 cm 2

 

Area of circle - Part 11

∴ Area is 1386 cm 2

 

Find area of a circle with radius 5 cm

Area of circle - Part 12

Radius = r

 = 5 cm

 

Now,

  Area = πœ‹ r 2

  = 3.14 × (5) 2

  = 3.14 × 25

  = 314/100 × 25

  = 314/20 × 5

  = 314/4 × 1

  = 157/2

  = 78.5 cm 2

∴ Area is 78.5 cm 2

 

Find the area of a circle with diameter 30 cm

Area of circle - Part 13

Diameter = 30 cm

Radius = r = Diameter/2

= 30/2 cm

= 15 cm

 

Now,

  Area = πœ‹ r 2

   = 3.14 × (15) 2

  = 3.14 × 225

  = 314/100 × 225

  = 314/20 × 45

  = 157/10 × 45

  = 7065/10

  = 706.5 cm 2

∴ Area = 706.5 cm 2

 

 

 

 

 

 

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.