# Example 10 - Chapter 8 Class 12 Application of Integrals (Important Question)

Last updated at May 29, 2018 by Teachoo

Last updated at May 29, 2018 by Teachoo

Transcript

Example 10 Find the area of the region enclosed between the two circles: 𝑥2+𝑦2=4 and 𝑥 –22+𝑦2=4 First we find center and radius of both circles Drawing figure Area required = Area OACA’ Area required = Area ACA’D + Area OADA’ Finding point of intersection, A & A’ Solving 𝑥2 + 𝑦2 = 4 …(1) ( 𝑥−2)2 + 𝑦2 = 4 …(2) Comparing (1) & (2) 𝑥2 + 𝑦2 = (x − 2)2 + 𝑦2 𝑥2 = (x − 2)2 𝑥2 − (x − 2)2 = 0 (x − (x − 2) (x + (x − 2)) = 0 (x − x + 2) (x + x − 2) = 0 2(2x − 2) = 0 (2x − 2) = 02 2x − 2 = 0 2x = 2 x = 22 x = 1 Put x = 1 in (1) 𝑥2 + 𝑦2 = 4 12 + 𝑦2 = 4 1 + 𝑦2 = 4 𝑦2 = 4 − 1 𝑦2 = 3 y = ± 3 So, points are (1, 3) & (1, – 3) Hence A = (1, 3) & A’ = (1, – 3) Also, D = (1, 0) Area required Area required = Area ACA’D + Area OADA’ Area ACA’D Area ACA’D = 2 Area ADC = 2 12𝑦 𝑑𝑥 Here, 𝑥2+ 𝑦2=4 𝑦2=4− 𝑥2 𝑦=± 4− 𝑥2 Since Area ADC is in 1st quadrant, y = 4− 𝑥2 Area ACA’D = 2 12𝑦 𝑑𝑥 = 2 12 4− 𝑥2 𝑑𝑥 =2 12 22− 𝑥2 𝑑𝑥 =2 𝑥2 22− 𝑥2+ 222 sin−1 𝑥212 = 2 𝑥2 4− 𝑥2+2 sin−1 𝑥212 =2 22 4− 22+2 sin−1 22− 12 4− 12+2 sin−1 12 =2 1. 4−4+2 sin−11− 12 4−1+2 sin−1 12 =2 1.0+ 2𝜋21− 12 3+ 2𝜋6 =2 𝜋− 32− 𝜋3 =2 2𝜋3− 32 = 𝟒𝝅𝟑− 𝟑 Area OADA’ Area OADA’ =2 × Area OAD = 2 01𝑦 𝑑𝑥 Here, 𝑥−22+ 𝑦2=4 𝑦2=4− 𝑥−22 𝑦=± 4− 𝑥−22 Since OAD is in 1st quadrant, 𝑦= 4− 𝑥−22 Hence, Area OADA’ = 2 01𝑦 𝑑𝑥 = 2 01 4− 𝑥−22 𝑑𝑥 Putting t = 𝑥−2 Diff. w.r.t. 𝑥 𝑑𝑡𝑑𝑥=1 𝑑𝑡 =𝑑𝑥 So, = 2 01 4− 𝑥−22 𝑑𝑥 =2 − 2− 1 4− 𝑡2 𝑑𝑡 =2 𝑡2 22− 𝑡2+ 222 sin−1 𝑡2−2−1 = 2 −1 2 22− −12+2 sin−1 −1 2− −2 2 22− −12+2 sin−1 −2 2 = 2 −1 2 4−1+2 sin−1 −1 2− −1 22− 22+2 sin−1(−1) = 2 −1 2 3− 2𝜋6−0+ 2𝜋2 =2 − 3 2+ 2𝜋3 = – 3 + 4𝜋3 Therefore, Area required = Area ACA’D + Area OADA’ = 4𝜋3− 3 + – 3 + 4𝜋3 = 8𝜋3−2 3

Chapter 8 Class 12 Application of Integrals

Class 12

Important Questions for exams Class 12

- Chapter 1 Class 12 Relation and Functions
- Chapter 2 Class 12 Inverse Trigonometric Functions
- Chapter 3 Class 12 Matrices
- Chapter 4 Class 12 Determinants
- Chapter 5 Class 12 Continuity and Differentiability
- Chapter 6 Class 12 Application of Derivatives
- Chapter 7 Class 12 Integrals
- Chapter 8 Class 12 Application of Integrals
- Chapter 9 Class 12 Differential Equations
- Chapter 10 Class 12 Vector Algebra
- Chapter 11 Class 12 Three Dimensional Geometry
- Chapter 12 Class 12 Linear Programming
- Chapter 13 Class 12 Probability

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Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.