NCERT Solutions for Class 9 Maths Exercise 4.2 Chapter 4 Linear Equation In Two Variables

The concept that is being discussed in detail under section 4.2 of the chapter “Linear Equations In Two Variables” is that a linear equation in two variables has infinitely many solutions. Exercise 4.2 that follows contains questions that will explain this concept a bit more clearly. NCERT Solutions have been designed by subject experts. This NCERT Solutions for Class 9 Maths Chapter 4- Linear Equations In Two Variables Exercise 4.2 was developed with an aim to help the students to learn the subject more thoroughly.

Designed as per the Class 9 syllabus and NCERT guidelines, these NCERT Solutions for Class 9 Maths Chapter 4- Linear Equations is accurate and is prepared after proper research. It helps students to comprehend the concepts well. It uses clear and lucid language to elucidate the topic.

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Access other exercise solutions of class 9 Maths Chapter 4- Linear Equations In Two Variables

Exercise 4.1 Solutions

Exercise 4.3 Solutions

Exercise 4.4 Solutions

NCERT Solutions for class 9 Maths Chapter 4- Linear Equations In Two Variables Exercise 4.2

1. Which one of the following options is true, and why?

y = 3x+5 has

  1. A unique solution
  2. Only two solutions
  3. Infinitely many solutions

Solution:

Let us substitute different values for x in the linear equation y = 3x+5,

x 0 1 2 …. 100
y, where y=3x+5 5 8 11 …. 305

From the table, it is clear that x can have infinite values, and for all the infinite values of x, there are infinite values of y as well.

Hence, (iii) infinitely many solutions is the only option true.

2. Write four solutions for each of the following equations:

(i) 2x+y = 7

Solution:

To find the four solutions of 2x+y =7 we substitute different values for x and y

Let x = 0

Then,

2x+y = 7

(20)+y = 7

y = 7

(0,7)

Let x = 1

Then,

2x+y = 7

(2×1)+y = 7

2+y = 7

y = 7-2

y = 5

(1,5)

Let y = 1

Then,

2x+y = 7

(2x)+1 = 7

2x = 7-1

2x = 6

x = 6/2

x = 3

(3,1)

Let x = 2

Then,

2x+y = 7

(2×2)+y = 7

4+y = 7

y =7-4

y = 3

(2,3)

The solutions are (0, 7), (1,5), (3,1), (2,3)

(ii) πx+y = 9

Solution:

To find the four solutions of πx+y = 9 we substitute different values for x and y

Let x = 0

Then,

πx+y = 9

(π0)+y = 9

y = 9

(0,9)

Let x = 1

Then,

πx +y = 9

(π×1)+y = 9

π+y = 9

y = 9-

(1, 9-)

Let y = 0

Then,

πx+y = 9

πx+0 = 9

πx = 9

x = 9/

(9/,0)

Let x = -1

Then,

πx + y = 9

(×-1) + y = 9

-+y = 9

y = 9+π

(-1,9+)

The solutions are (0,9), (1,9-), (9/,0), (-1,9+)

(iii) x = 4y

Solution:

To find the four solutions of x = 4y we substitute different values for x and y

Let x = 0

Then,

x = 4y

0 = 4y

4y= 0

y = 0/4

y = 0

(0,0)

Let x = 1

Then,

x = 4y

1 = 4y

4y = 1

y = 1/4

(1,1/4)

Let y = 4

Then,

x = 4y

x= 4×4

x = 16

(16,4)

Let y =

Then,

x = 4y

x = 4×1

x = 4

(4,1)

The solutions are (0,0), (1,1/4), (16,4), (4,1)

3. Check which of the following are solutions of the equation x–2y = 4 and which are not:

(i) (0, 2)

(ii) (2, 0)

(iii) (4, 0)

(iv) (√2, 4√2)

(v) (1, 1)

Solutions:

(i) (0, 2)

(x,y) = (0,2)

Here, x=0 and y=2

Substituting the values of x and y in the equation x–2y = 4, we get,

x–2y = 4

⟹ 0 – (2×2) = 4

But, -4 4

(0, 2) is not a solution of the equation x–2y = 4

(ii) (2, 0)

(x,y) = (2, 0)

Here, x = 2 and y = 0

Substituting the values of x and y in the equation x -2y = 4, we get,

x -2y = 4

⟹ 2-(2×0) = 4

⟹ 2 -0 = 4

But, 2 ≠ 4

(2, 0) is not a solution of the equation x-2y = 4

(iii) (4, 0)

Solution:

(x,y) = (4, 0)

Here, x= 4 and y=0

Substituting the values of x and y in the equation x -2y = 4, we get,

x–2y = 4

⟹ 4 – 2×0 = 4

⟹ 4-0 = 4

⟹ 4 = 4

(4, 0) is a solution of the equation x–2y = 4

(iv) (√2,4√2)

Solution:

(x,y) = (√2,4√2)

Here, x = √2 and y = 4√2

Substituting the values of x and y in the equation x–2y = 4, we get,

x –2y = 4

⟹ √2-(2×4√2) = 4

√2-8√2 = 4

But, -7√2 ≠ 4

(√2,4√2) is not a solution of the equation x–2y = 4

(v) (1, 1)

Solution:

(x,y) = (1, 1)

Here, x= 1 and y= 1

Substituting the values of x and y in the equation x–2y = 4, we get,

x –2y = 4

⟹ 1 -(2×1) = 4

⟹ 1-2 = 4

But, -1 ≠ 4

(1, 1) is not a solution of the equation x–2y = 4

4. Find the value of k, if x = 2, y = 1 is a solution of the equation 2x+3y = k.

Solution:

The given equation is

2x+3y = k

According to the question, x = 2 and y = 1.

Now, Substituting the values of x and y in the equation2x+3y = k,

We get,

(2×2)+(3×1) = k

⟹ 4+3 = k

⟹ 7 = k

k = 7

The value of k, if x = 2, y = 1 is a solution of the equation 2x+3y = k, is 7.


Now, a student is well aware from earlier lessons that a linear equation in one variable has a unique solution. However, what about the solution of a linear equation involving two variables? Exercise 4.2 of Chapter 4 from NCERT textbook tries to explain this concept to you with the help of some solved examples and about 4 questions. To make it easier for the students to follow the concept and learn in thoroughly, we have given step by step explanation in the NCERT Solutions for Class 9 Maths.

Question number 1 has a main question followed by 3 sub-questions, while question number two is also of the same format. Meanwhile, question number 3 is of MCQ format and Question number 4 is a short answer question.

Solving these help the students to be more confident while writing exams. Other benefits are as follows:

  • Help students to get practice in solving a variety of maths problems
  • Gain efficiency and accuracy in solving questions
  • Get good scores in mathematics as they understand the subject better
  • Understand the concepts more clearly

1 Comment

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