The region inside the circle is called its area. The formula to find the area is Area = π x r

The unit of area is m

1) Find the area of a circle of radius 4.2 cm.

Area = 3.14 x (4.2)

= 55.44 cm

_________________________________________________________________

2) A copper wire, when bent in the form of a square, encloses an area of 484 cm

⇒ (side )

⇒ Side = 22 cm

So, the perimeter of square = 4 x side = 4 x 22 = 88 cm

Circumference of a circle = Perimeter of square

⇒ 2 x π x r = 88

⇒ 2 x 3.14 x r = 88

⇒ r = 14 cm

Area of circle = π x r

Area = 616 cm

_________________________________________________________________

3) PQRS is a diameter of a circle of radius 6 cm. The lengths PQ,QR and RS are equal. Semicircles are drawn on PQ and QS as diameters.Find the area of the shaded region.

As PQ = QR =RS

∴ PQ =QR =RS = 1/3 x PS = 1/3 x 12 = 4 cm.

QS = 2 PQ

QS = 2 x 4 = 8 cm

∴ Area of shaded region = Area of semicircle with PS as diameter + Area of semicircle with PQ as diameter – Area of semicircle with QS as diameter.

= ½ [ 3.14 x 6

= ½ [ 3.14 x 36 + 3.14 x 4 – 3.14 x 16 ]

= ½ [ 3.14 ( 36 + 4 – 16)]

= ½ ( 3.14 x 24 ) = ½ x 75.36

∴ Area of shaded region = 37.68 cm

_________________________________________________________________

• Circumference of Circle

• Area of Circle

7th grade math

Home

GMAT

GRE

1st Grade

2nd Grade

3rd Grade

4th Grade

5th Grade

6th Grade

7th grade math

8th grade math

9th grade math

10th grade math

11th grade math

12th grade math

Precalculus

Worksheets

Chapter wise Test

MCQ's

Math Dictionary

Graph Dictionary

Multiplicative tables

Math Teasers

NTSE

Chinese Numbers

CBSE Sample Papers