## NCERT Solutions for Class 12 Maths Chapter 8 – Application of Integrals Ex 8.2

#### Page No 371:

#### Question 1:

Find the area of the circle 4

*x*^{2}+ 4*y*^{2}= 9 which is interior to the parabola*x*^{2}= 4*y*#### Answer:

The required area is represented by the shaded area OBCDO.

Solving the given equation of circle, 4

*x*^{2}+ 4*y*^{2}= 9, and parabola,*x*^{2}= 4*y*, we obtain the point of intersection as.
It can be observed that the required area is symmetrical about

*y*-axis.
∴ Area OBCDO = 2 × Area OBCO

We draw BM perpendicular to OA.

Therefore, the coordinates of M are.

Therefore, Area OBCO = Area OMBCO – Area OMBO

=∫02(9-4×2)4dx-∫02x24dx

=∫02322-x2dx-14∫02x2dx

=x2322-x2+98sin-12×302-14×3302

=24+98sin-1223-11223

=122+98sin-1223-132

=162+98sin-1223

=1226+94sin-1223Therefore, the required area OBCDO is units

#### Question 2:

Find the area bounded by curves (

*x*– 1)^{2}+*y*^{2}= 1 and*x*^{2}+*y*^{ 2}= 1#### Answer:

The area bounded by the curves, (

*x*– 1)^{2}+*y*^{2}= 1 and*x*^{2}+*y*^{ 2}= 1, is represented by the shaded area as
On solving the equations, (

*x*– 1)^{2}+*y*^{2}= 1 and*x*^{2}+*y*^{ 2}= 1, we obtain the point of intersection as Aand B.
It can be observed that the required area is symmetrical about

*x*-axis.
∴ Area OBCAO = 2 × Area OCAO

We join AB, which intersects OC at M, such that AM is perpendicular to OC.

The coordinates of M are .

Therefore, required area OBCAO = units

#### Question 3:

Find the area of the region bounded by the curves

*y*=*x*^{2 }+ 2,*y*=*x*,*x*= 0 and*x*= 3#### Answer:

The area bounded by the curves,

*y*=*x*^{2 }+ 2,*y*=*x*,*x*= 0, and*x*= 3, is represented by the shaded area OCBAO as
Then, Area OCBAO = Area ODBAO – Area ODCO

#### Question 4:

Using integration finds the area of the region bounded by the triangle whose vertices are (–1, 0), (1, 3) and (3, 2).

#### Answer:

BL and CM are drawn perpendicular to

*x*-axis.
It can be observed in the following figure that,

Area (ΔACB) = Area (ALBA) + Area (BLMCB) – Area (AMCA) … (1)

Equation of line segment AB is

Equation of line segment BC is

Equation of line segment AC is

Therefore, from equation (1), we obtain

Area (ΔABC) = (3 + 5 – 4) = 4 units

#### Question 5:

Using integration find the area of the triangular region whose sides have the equations

*y*= 2*x*+1,*y*= 3*x*+ 1 and*x*= 4.#### Answer:

The equations of sides of the triangle are

*y*= 2*x*+1,*y*= 3*x*+ 1, and*x*= 4.
On solving these equations, we obtain the vertices of triangle as A(0, 1), B(4, 13), and C (4, 9).

It can be observed that,

Area (ΔACB) = Area (OLBAO) –Area (OLCAO)

#### Page No 372:

#### Question 6:

Smaller area enclosed by the circle

*x*^{2}+*y*^{2}= 4 and the line*x*+*y*= 2 is**A.**2 (π – 2)

**B.**π – 2

**C.**2π – 1

**D.**2 (π + 2)

#### Answer:

The smaller area enclosed by the circle,

*x*^{2}+*y*^{2}= 4, and the line,*x*+*y*= 2, is represented by the shaded area ACBA as
It can be observed that,

Area ACBA = Area OACBO – Area (ΔOAB)

Thus, the correct answer is B.

#### Question 7:

Area lying between the curve

*y*^{2}= 4*x*and*y*= 2*x*is**A.**

**B.**

**C.**

**D.**

#### Answer:

The area lying between the curve,

*y*^{2}= 4*x*and*y*= 2*x*, is represented by the shaded area OBAO as
The points of intersection of these curves are O (0, 0) and A (1, 2).

We draw AC perpendicular to

*x*-axis such that the coordinates of C are (1, 0).
âˆ´ Area OBAO = Area (OCABO) â€“ Area (Î”OCA)

square units

Thus, the correct answer is B.

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