Bseb and CBSE Ncert class 10 math chapter 12 solution and concept

Area related to circles

Perimeter and area of a circle

Perimeter (Circumference) 

The distance covered by travelling once around a circle its perimeter ,usually called its circumference.

• Circumference of a circle bears a constant ratio with its diameter. 
• This constant ratio is denoted by the Greek letter π(read as 'Pi') . 

In other words 

Area of circle=πr^2

Where r is radius of circle

Value of π=3.14

According to aaryabhata, π=3.1416

According to srinivas Ramanujan=3.14

And we take π=22/7

Solution of Ncert class 10 math exercise 12 All question solution

Example 1: 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 m^2. find the cost of ploughing the field(Take π=22/7) 

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Ncert class 10 math exercise 12.1 question 1

1.The radii of two circles are 19 cm and 9 cm respectively. Find the radius of the circle which has circumference equal to the sum of the circumference of the two circles.

Soln:- Given radius of circle first circle=19 cm

So, Circumference of first circle=2π×19 cm=38π

and radius of second circle=9 cm

So, Circumference of second circle=2π×9 cm=18π

According to question, 

let r be the radius of the circle which has circumference equal to the sum of the circumference of the two circles

So, 2πr= Circumference of first circle+Circumference of second circle

⇒2πr=38π+18π

⇒ 2πr=56π

⇒r=56π/2π

⇒r=28 cm