# RS Aggarwal Chapter 12 Class 9 Maths Exercises 12.2 (ex 12b) Solutions

RS Aggarwal Chapter 12 Class 9 Maths Exercise 12.2 Solutions: You may have come across many objects in daily life, which are round in shape, such as wheels of a vehicle, bangles, dials of many clocks, coins of denominations 50 p, Re 1 and Rs 5, key rings, buttons of shirts, etc.In a clock, you might have observed that the second’s hand goes round the dial of the clock rapidly and its tip moves in a round path. This path traced by the tip of the second’s hand is called a circle. In this chapter, you will study circles, other related terms and some properties of a circle.

EXERCISE 12B

## Important Definition for RS Aggarwal Chapter 12 Class 9 Maths Ex 12b Solutions

A circle is a closed geometrical figure. All points on the boundary of a circle are equidistance from a fixed point inside the circle (called the centre).

1. Area of a circle (of radius r) = π × r2
2. The diameter of the circle, d = 2 × r
3. Circumference of the circle = 2 × π × r
4. Sector angle of the circle, θ = (180 × l ) / (π × r )
5. Area of the sector = (θ/2) × r2; where θ is the angle between the two radii
6. Area of the circular ring = π × (R2– r2); where R – radius of the outer circle and r – radius of the inner circle

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