# NCERT Solutions Class 12 Maths Chapter 10 Vector Algebra

The NCERT Solutions for Class 12 Maths Chapter 10 Vector Algebra are given here where the students learn about the difference between a scalar and a vector quantity, their properties, operations of vectors, etc. The topic has an important role in helping the students score high marks not only in the board exams but also in the competitive exams. It is important to be prepared for the various problems asked during the 12th board examination. Solving through different exercises and problem sets give students the confidence to write the exams better. These Class 12 NCERT Solutions for Vector Algebra are very easy to understand. Students can also avail these NCERT Solutions and download it for free to practise them offline as well.

### NCERT Solutions for Class 12 Maths Chapter 10 – Vector Algebra

Exercise 10.1 Page No: 428

1. Represent graphically a displacement of 40 km, 30° east of north.

Solution:

The vector
represents the displacement of 40 km, 30o east of north.

2. Classify the following measures as scalars and vectors.

(i) 10 kg (ii) 2 metres north-west (iii) 40°

(iv) 40 watt (v) 10–19 coulomb (vi) 20 m/s2

Solution:

(i) 10 kg is a scalar quantity because it has only magnitude.

(ii) 2 meters north-west is a vector quantity as it has both magnitude and direction.

(iii) 40° is a scalar quantity as it has only magnitude.

(iv) 40 watts is a scalar quantity as it has only magnitude.

(v) 10–19 coulomb is a scalar quantity as it has only magnitude.

(vi) 20 m/s2 is a vector quantity as it has both magnitude and direction.

3. Classify the following as scalar and vector quantities.

(i) time period (ii) distance (iii) force

(iv) velocity (v) work done

Solution:

(i) Time period is a scalar quantity as it has only magnitude.

(ii) Distance is a scalar quantity as it has only magnitude.

(iii) Force is a vector quantity as it has both magnitude and direction.

(iv) Velocity is a vector quantity as it has both magnitude as well as direction.

(v) Work done is a scalar quantity as it has only magnitude.

4. In Figure, identify the following vectors.

(i) Coinitial (ii) Equal (iii) Collinear but not equal

Solution:

directions are not the same.

5. Answer the following as true or false.

(i)  andare collinear.

(ii) Two collinear vectors are always equal in magnitude.

(iii) Two vectors having same magnitude are collinear.

(iv) Two collinear vectors having the same magnitude are equal.

Solution:

(i) True.

Vectors
and
are parallel to the same line.

(ii) False.

Collinear vectors are those vectors that are parallel to the same line.

(iii) False.

Two vectors having the same magnitude need not necessarily be parallel to the same line.

(iv) False.

Only if the magnitude and direction of two vectors are the same, regardless of the positions of their initial points the two vector are said to be equal.

Exercise 10.2 Page No: 440

1. Compute the magnitude of the following vectors:

Solution:

Given vectors are:

2. Write two different vectors having same magnitude.

Solution:

3. Write two different vectors having same direction.

Solution:

Two different vectors having same directions are:

Let us

4. Find the values of x and y so that the vectors are equal

Solution:

Given vectors
will be equal only if their corresponding components are equal.

Thus, the required values of x and y are 2 and 3 respectively.

5. Find the scalar and vector components of the vector with initial point (2, 1) and terminal point (–5, 7).

Solution:

The scalar and vector components are:

The vector with initial point P (2, 1) and terminal point Q (–5, 7) can be shown as,

Thus, the required scalar components are –7 and 6 while the vector components are

6. Find the sum of the vectors

Solution:

Let us find the sum of the vectors:

7. Find the unit vector in the direction of the vector

Solution:

We know that

8. Find the unit vector in the direction of vector , where P and Q are the points

(1, 2, 3) and (4, 5, 6), respectively

Solution:

We know that,

9. For given vectors, and , find the unit vector in the direction of the vector

Solution:

We know that,

10. Find a vector in the direction of vector which has magnitude 8 units.

Solution:

Firstly,

11. Show that the vectorsare collinear.

Solution:

Firstly,

Therefore, we can say that the given vectors are collinear.

12. Find the direction cosines of the vector

Solution:

Firstly,

13. Find the direction cosines of the vector joining the points A (1, 2, –3) and

B (–1, –2, 1) directed from A to B.

Solution:

We know that the

Given points are A (1, 2, –3) and B (–1, –2, 1).

Now,

14. Show that the vector is equally inclined to the axes OX, OY, and OZ.

Solution:

Firstly,

15. Find the position vector of a point R which divides the line joining two points P and Q whose position vectors are  respectively, in the ratio 2:1

(i) internally

(ii) externally

Solution:

We know that

The position vector of point R dividing the line segment joining two points

P and Q in the ratio m: is given by:

16. Find the position vector of the mid point of the vector joining the points P (2, 3, 4) and Q (4, 1, – 2).

Solution:

The position vector of mid-point R of the vector joining points P (2, 3, 4) and Q (4, 1, – 2) is given by,

17. Show that the points A, B and C with position vectors,respectively form the vertices of a right angled triangle.

Solution:

We know

Given position vectors of points A, B, and C are:

Hence, proved that the given points form the vertices of a right angled triangle.

18. In triangle ABC (Fig 10.18) which of the following is not true:

Solution:

Firstly let us consider,

19. If are two collinear vectors, then which of the following are incorrect:

A. , for some scalar λ

B.

C. the respective components of are proportional

D. both the vectors have same direction, but different magnitudes

Solution:

We know

Exercise 10.3 Page No: 447

1. Find the angle between two vectorsandwith magnitudes √3 and 2, respectively having.

Solution:

Firstly let us consider,

2. Find the angle between the vectors

Solution:

Let us consider the

Hence, the angle between the vectors is cos-1 (5/7).

3. Find the projection of the vectoron the vector.

Solution:

Firstly,

4. Find the projection of the vectoron the vector.

Solution:

Firstly,

Hence, the projection is 60/114.

5. Show that each of the given three vectors is a unit vector:

Also, show that they are mutually perpendicular to each other.

Solution:

It is given that

6. Find

Solution:

Let us consider,

7. Evaluate the product

Solution:

Let us consider the given expression,

8. Find the magnitude of two vectors, having the same magnitude and such that the angle between them is 60° and their scalar product is ½.

Solution:

Firstly,

Hence the magnitude of two vectors is 1.

Solution:

Let us consider,

Hence the value is 13.

10. Ifare such thatis perpendicular to, then find the value of λ.

Solution:

We know that the

11. Show that is perpendicular to, for any two nonzero vectors.

Solution:

Let us consider,

12. If, then what can be concluded about the vector?

Solution:

We know

13. If are unit vectors such that , find the value of .

Solution:

Consider the given vectors,

Hence the value is -3/2.

14. If either vector, then. But the converse need not be true. Justify your answer with an example.

Solution:

Firstly,

15. If the vertices A, B, C of a triangle ABC are (1, 2, 3), (–1, 0, 0), (0, 1, 2), respectively, then find ∠ABC. [∠ABC is the angle between the vectorsand]

Solution:

We know

Hence, the angle is cos-1 (10/102).

16. Show that the points A (1, 2, 7), B (2, 6, 3) and C (3, 10, –1) are collinear.

Solution:

Let us consider

Given points are A (1, 2, 7), B (2, 6, 3), and C (3, 10, –1).

Now,

Therefore, the given points A, B, and C are collinear.

17. Show that the vectorsform the vertices of a right angled triangle.

Solution:

Firstly consider,

Solution:

Explanation:

Exercise 10.4 Page No: 454

1. Find, if and

Solution:

It is given that,

2. Find a unit vector perpendicular to each of the vector and, where and.

Solution:

It is given that,

Solution:

Firstly,

4. Show that

Solution:

Firstly consider the LHS,

We have,

5. Find λ and μ if .

Solution:

It is given that,

Solution:

It is given that,

Solution:

Firstly let us consider,

9. Find the area of the triangle with vertices A (1, 1, 2), B (2, 3, 5) and C (1, 5, 5).

Solution:

We know,

10. Find the area of the parallelogram whose adjacent sides are determined by the vector .

Solution:

Let us consider,

Solution:

Explanation:

12. Area of a rectangle having vertices A, B, C, and D with position vectors and  respectively is

Solution:

Explanation:

Miscellaneous Exercise Page No: 458

1. Write down a unit vector in XY-plane, making an angle of 30° with the positive direction of x-axis.

Solution:

Let us consider,

2. Find the scalar components and magnitude of the vector joining the points P (x1, y1, z1) and Q (x2, y2, z2).

Solution:

Firstly let us consider,

3. A girl walks 4 km towards west, then she walks 3 km in a direction 30° east of north and stops. Determine the girl’s displacement from her initial point of departure.

Solution:

It is given that,

Let O and B be the initial and final positions of the girl respectively.

Then, the girl’s position can be shown as:

Solution:

It is given that,

5. Find the value of x for whichis a unit vector.

Solution:

We know,

6. Find a vector of magnitude 5 units, and parallel to the resultant of the vectors

.

Solution:

Let us consider the,

7. If, find a unit vector parallel to the vector.

Solution:

Let us consider the given vectors,

8. Show that the points A (1, –2, –8), B (5, 0, –2) and C (11, 3, 7) are collinear, and find the ratio in which B divides AC.

Solution:

Firstly let us consider,

9. Find the position vector of a point R which divides the line joining two points P and Q whose position vectors areexternally in the ratio 1: 2. Also, show that P is the midpoint of the line segment RQ.

Solution:

We know,

10. The two adjacent sides of a parallelogram areand .

Find the unit vector parallel to its diagonal. Also, find its area.

Solution:

Firstly let us consider,

11. Show that the direction cosines of a vector equally inclined to the axes OX, OY and OZ are.

Solution:

Firstly,

Let’s assume a vector to be equally inclined to axes OX, OY, and OZ at angle α.

Then, the direction cosines of the vector are cos α, cos α, and cos α.

Now, we know that

Therefore, the direction cosines of the vector which are equally inclined to the axes are

Hence proved.

Solution:

Assume,

13. The scalar product of the vectorwith a unit vector along the sum of vectors and is equal to one. Find the value of.

Solution:

Let’s consider the

14. If are mutually perpendicular vectors of equal magnitudes, show that the vector is equally inclined to and.

Solution:

Lets assume,

Hence proved.

15. Prove that, if and only if are perpendicular, given.

Solution:

It is given that

Hence proved.

Solution:

Explanation:

Solution:

Explanation:

Hence the correct answer is D.

18. The value of is

(A) 0 (B) –1 (C) 1 (D) 3

Solution:

Explanation:

It is given that,

Hence the correct answer is C.

Solution:

Explanation:

 Also Access NCERT Exemplar for Class 12 Maths Chapter 10 CBSE Notes for Class 12 Maths Chapter 10

The major concepts of Maths covered in Chapter 10- Vector Algebra of NCERT Solutions for Class 12 includes: 10.1 Introduction 10.2 Basic Concepts

• Position Vector
• Direction Cosines

10.3 Types of Vectors

• Zero Vector
• Unit Vector
• Coinitial Vectors
• Collinear Vectors
• Equal Vectors
• Negative of a Vector

10.5 Multiplication of a Vector by a Scalar 10.5.1 Components of a vector 10.5.2 Vector joining two points 10.5.3 Section formula 10.6 Product of Two Vectors 10.6.1 Scalar (or dot) product of two vectors 10.6.2 Projection of a vector on a line 10.6.3 Vector (or cross) product of two vectors
Exercise 10.1 Solutions 5 Questions
Exercise 10.2 Solutions 19 Questions
Exercise 10.3 Solutions 18 Questions
Exercise 10.4 Solutions 12 Questions
Miscellaneous Exercise On Chapter 10 Solutions 19 Questions

## NCERT Solutions for Class 12 Maths Chapter 10- Vector Algebra

The chapter Vector Algebra belongs to the unit Vectors and Three – Dimensional Geometry, that adds up to 14 marks of the total marks. There are 4 exercises along with a miscellaneous exercise in this chapter to help students understand the concepts related to Vectors and Vector Algebra clearly. Some of the topics discussed in the tenth Chapter of NCERT Solutions for Class 12 Maths are as follows:

1. The scalar components of a vector are its direction ratios and represent its projections along the respective axes.
2. The magnitude (r), direction ratios (a, b, c) and direction cosines (l, m, n) of any vector are related as l=(a/r), m=(b/r) n=(c/r)
3. The vector sum of the three sides of a triangle taken in order is 0.
4. The vector sum of two coinitial vectors is given by the diagonal of the parallelogram whose adjacent sides are the given vectors.
5. The multiplication of a given vector by a scalar λ, changes the magnitude of the vector by the multiple |λ|, and keeps the direction same (or makes it opposite) accordingly as the value of λ is positive (or negative).

The other concepts and topics explained in the chapter can be understood by going through Chapter 10 of the NCERT textbook for Class 12.

### Key Features of NCERT Solutions for Class 12 Maths Chapter 10- Vector Algebra

Studying the Vector Algebra of Class 12 enables the students to understand the following: Vectors and scalars, magnitude and direction of a vector. Direction cosines and direction ratios of a vector. Types of vectors (equal, unit, zero, parallel and collinear vectors), position vector of a point, negative of a vector, components of a vector, the addition of vectors, multiplication of a vector by a scalar, position vector of a point dividing a line segment in a given ratio. Definition, Geometrical Interpretation, properties and application of scalar (dot) product of vectors, vector (cross) product of vectors, scalar triple product of vectors.

## Frequently Asked Questions on NCERT Solutions for Class 12 Maths Chapter 10

### How many questions are present in each exercise of NCERT Solutions for Class 12 Maths Chapter 10?

The number of question in each exercise of NCERT Solutions for Class 12 Maths Chapter 10 are:
Exercise 10.1 – 5 Questions
Exercise 10.2 – 19 Questions
Exercise 10.3 – 18 Questions
Exercise 10.4 – 12 Questions
Miscellaneous Exercise – 19 Questions

### What are the major concepts discussed in NCERT Solutions for Class 12 Maths Chapter 10?

The major concepts discussed in NCERT Solutions for Class 12 Maths Chapter 10 are:
10.1 – Introduction
10.2 – Basic Concepts
10.3 – Types of Vectors