# NCERT solution class 12 chapter 4 Differential Equations exercise 4.4 mathematics part 2

## EXERCISE 4.4

Find, if and.

We have,

and

#### Question 2:

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

We have,

and

Hence, the unit vector perpendicular to each of the vectors and is given by the relation,

#### Question 3:

If a unit vector  makes an angleswith with and an acute angle θ with, then find θ and hence, the compounds of.

Let unit vector  have (a1a2a3) components.

⇒

Since  is a unit vector, .

Also, it is given that  makes angleswith with , and an acute angle θ with

Then, we have:

Hence, and the components of  are.

Show that

#### Question 5:

Find λ and μ if .

On comparing the corresponding components, we have:

Hence,

#### Question 6:

Given that  and. What can you conclude about the vectors?

Then,

(i) Either  or, or

(ii) Either  or, or

But,  and  cannot be perpendicular and parallel simultaneously.

Hence,  or.

#### Question 7:

Let the vectors given as . Then show that

We have,

On adding (2) and (3), we get:

Now, from (1) and (4), we have:

Hence, the given result is proved.

#### Question 8:

If either  or, then. Is the converse true? Justify your answer with an example.

Take any parallel non-zero vectors so that.

It can now be observed that:

Hence, the converse of the given statement need not be true.

#### Question 9:

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

C (1, 5, 5).

The vertices of triangle ABC are given as A (1, 1, 2), B (2, 3, 5), and

C (1, 5, 5).

The adjacent sidesand of ΔABC are given as:

Area of ΔABC

Hence, the area of ΔABC

#### Question 10:

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

The area of the parallelogram whose adjacent sides are is.

Hence, the area of the given parallelogram is.

#### Question 11:

Let the vectors and be such that and, then is a unit vector, if the angle between and is

(A)  (B)  (C)  (D)

It is given that.

We know that, where  is a unit vector perpendicular to both and and θ is the angle between and.

Now,  is a unit vector if.

Hence,  is a unit vector if the angle between and is.

#### Question 12:

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

(A)  (B) 1

(C) 2 (D)

The position vectors of vertices A, B, C, and D of rectangle ABCD are given as:

The adjacent sides and  of the given rectangle are given as:

⇒AB→×BC→=2Now, it is known that the area of a parallelogram whose adjacent sides are is.

Hence, the area of the given rectangle is