# Vector Algebra For Class 12

## Vector Algebra Introduction

In Mathematics, the topic vector algebra for class 12 is all about in-depth studying of scalars and vectors. A lot of quantities have magnitude as well as direction.

A quantity is known as a vector quantity if they have a direction as well as magnitude. A quantity is known as scalar quantity if it has only magnitude. Some examples of the vector quantities are acceleration, velocity, displacement, force, momentum, weight, and more. In this article, you will be studying vector algebra for class 12. It covers concepts such as position vector, types of vectors, the operation that is performed on vectors, and some solved examples to understand the concept better.

### Vector Algebra Concepts

The physical quantities having direction and magnitude is described using the concept of vectors. A scalar quantity just has a number or has only a constant. Important concepts in vector algebra for class 12 NCERT syllabus are vector definition, position vector, types of vectors, the operation that is performed on vectors, solved examples, multiplication of a vector with a scalar quantity, and multiplication of two vectors.

### Vector Algebra Notes

Position Vector

With respect to the origin O ( 0, 0, 0 ), the position vector is given, where the coordinate of point K is given as K ( x, y, z). The formula goes by:

$\overline{OK} = \sqrt{x^{2} + y^{2} + z^{2}}$

### The Relation Between Direction Ratios, Direction Cosines and Magnitude

The direction ratios ( l, m, n ),  the magnitude ( s ), and the direction cosines ( u, v, w ) of any vector that is related are given as u = $\frac{l}{s}$, v = $\frac{m}{s}$, n = $\frac{w}{ s}$.

### Different Types of Vectors

The different types of vectors in vector algebra are:

• Zero Vector

• Unit Vector

• Coinitial Vector

• Collinear Vector

• Equal Vector

• Negative of a Vector

### Operations on Two Vectors

The operations that can be performed on two vectors are addition, multiplication, and subtraction. Now, let’s understand how these operations are applied to the vectors.

### Dot Product or Multiplication of Vectors

The dot product of the vector is calculated with the help of a dot. It is represented as shown below:

j . k

Now, the dot product can be represented in two different ways:

l . m = | l | x | m | x cos Ө

Here,

| l | - is the length (the magnitude) of vector l.

| m | - is the length (the magnitude) of vector m.

Ө - the angle between l and m.

To find the dot product of vector l and vector m, we multiply the length of l = | l | and the  length of m = | m |

The other way to calculate the dot product is:

l . m = lx + mx + ly + my

First, the x values are multiplied with each other. Next, the y values are multiplied, and then they are added together.

Consider two vectors: PQ and QR. Here, the ending point of the first vector is the starting point of the second vector.  Hence, the sum of two vectors is represented as:

$\overline{PR} = \overline{PQ} + \overline{QR}$

This is also known as the triangle law of addition of vectors and is used when one needs to find the sum of two or more vectors.

### Solved Examples

Question 1: The direction of a vector is $\overline{v} = 4\widehat{i} + 5\widehat{j} + 6\widehat{k}$. Find the unit vector.

Solution:

The unit vector in the direction of a vector $\overline{v}$ is known as $\widehat{v} = \frac{1}{|a|}\times \overline{v}$

Hence, $|\overline{v}| = \sqrt{4^{2} + 5^{2} + 6^{2}} = \sqrt{77}$

Therefore, $\widehat{v} = \frac{1}{\sqrt{77}} (4\widehat{i} + 5\widehat{j} + 6\widehat{k})$

$\widehat{v} = \frac{4}{\sqrt{77}}\widehat{i} + \frac{5}{\sqrt{77}}\widehat{j} + \frac{6}{\sqrt{77}}\widehat{k}$

Question 2: The direction of a vector is $\overline{v} = 1\widehat{i} + 7\widehat{j} + 4\widehat{k}$. Find the unit vector.

Solution:

The unit vector in the direction of a vector $\overline{v}$ is known as $\widehat{v} = \frac{1}{|a|}\times \overline{v}$

Hence, $|\overline{v}| = \sqrt{1^{2} + 7^{2} + 4^{2}} = \sqrt{66}$

Therefore, $\widehat{v} = \frac{1}{\sqrt{66}} (1\widehat{i} + 7\widehat{j} + 4\widehat{k})$

$\widehat{v} = \frac{1}{\sqrt{66}}\widehat{i} + \frac{7}{\sqrt{66}}\widehat{j} + \frac{4}{\sqrt{66}}\widehat{k}$

Question 3: The direction of a vector is $\overline{v} = 3\widehat{i} + 2\widehat{j} + 3\widehat{k}$. Find the unit vector.

Solution:

The unit vector in the direction of a vector $\overline{v}$ is known as $\overline{v}$ is known as $\widehat{v} = \frac{1}{|a|}\times \overline{v}$

Hence, $|\overline{v}| = \sqrt{3^{2} + 2^{2} + 3^{2}} = \sqrt{22}$

Therefore, $\widehat{v} = \frac{1}{\sqrt{22}} (3\widehat{i} + 2\widehat{j} + 3\widehat{k})$

$\widehat{v} = \frac{3}{\sqrt{22}}\widehat{i} + \frac{2}{\sqrt{22}}\widehat{j} + \frac{3}{\sqrt{22}}\widehat{k}$

1) How to Calculate the Dot Product of Two Vectors?

The dot product of the vector is calculated with the help of a dot. It is represented as shown below j. k

Now, the dot product can be represented in two different ways:

l. m = | l | x | m | x cos Ө

Here,

| l | - is the length (the magnitude) of vector l.

| m | - is the length (the magnitude) of vector m.

Ө - the angle between l and m.

To find the dot product of vector l and vector m, we multiply the length of l = | l | and the  length of m = | m |

The other way to calculate the dot product is:

l. m = lx + mx + ly + my

First, the x values are multiplied with each other. Next, the y values are multiplied and then they are added together.