Q9 of 31 Page 178

The area enclosed between two concentric circles is:


Let the radius of the smaller circle be r and radius of the larger circle be R.


The area enclosed between two concentric circles = Area of the larger circle – area of the smaller circle


∵The area of a circle = πr2


⇒ Required area = πR2 - πr2


⇒ Required area = π (R2 - r2)


Using (a+b)(a-b) = a2 - b2


⇒ Required area = π (R+r)(R-r)

More from this chapter

All 31 →
7

The cost of fencing a circular field at the rate of 24 per metre is 5280. The field is to be ploughed at the rate of 0.50 per m2. Find the cost of ploughing the field.

 8

The radius of a circular grass field is 35 m. There is a 7 m wide path all around it. Find the area of the path.

 10

The radii of two concentric circles are 4 cm and 3 cm respectively. The area enclosed by the two circles is:

 1

In a circle of radius 7 cm, an arc subtends an angle of 60° at the centre. Find the length of the arc.