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Linear Equations in One Variable (Exercise 8.1) RD Sharma Solutions | Mathematics (Maths) Class 7 PDF Download

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 Page 1


 
 
 
 
 
 
 
Exercise 8.1        Page No: 8.6 
 
1. Verify by substitution that: 
(i) x = 4 is the root of 3x – 5 = 7 
(ii) x = 3 is the root of 5 + 3x = 14 
(iii) x = 2 is the root of 3x – 2 = 8x – 12 
(iv) x = 4 is the root of (3x/2) = 6 
(v) y = 2 is the root of y – 3 = 2y – 5 
(vi) x = 8 is the root of (1/2)x + 7 = 11 
 
Solution: 
(i) Given x = 4 is the root of 3x - 5 = 7 
Now, substituting x = 4 in place of ‘x’ in the given equation, we get 
= 3(4) – 5 = 7 
= 12 – 5 = 7 
7 = 7 
Since, LHS = RHS 
Hence, x = 4 is the root of 3x - 5 = 7. 
 
(ii) Given x = 3 is the root of 5 + 3x = 14. 
Now, substituting x = 3 in place of ‘x’ in the given equation, we get 
= 5 + 3(3) = 14 
= 5 + 9 = 14 
14 = 14 
Since, LHS = RHS 
Hence, x = 3 is the root of 5 + 3x = 14. 
 
(iii) Given x = 2 is the root of 3x – 2 = 8x – 12. 
Now, substituting x = 2 in place of ‘x’ in the given equation, we get 
= 3(2) – 2 = 8(2) – 12 
= 6 – 2 = 16 – 12 
4 = 4 
Since, LHS = RHS 
Hence, x = 2 is the root of 3x – 2 = 8x – 12. 
 
(iv) Given x = 4 is the root of 3x/2 = 6. 
Page 2


 
 
 
 
 
 
 
Exercise 8.1        Page No: 8.6 
 
1. Verify by substitution that: 
(i) x = 4 is the root of 3x – 5 = 7 
(ii) x = 3 is the root of 5 + 3x = 14 
(iii) x = 2 is the root of 3x – 2 = 8x – 12 
(iv) x = 4 is the root of (3x/2) = 6 
(v) y = 2 is the root of y – 3 = 2y – 5 
(vi) x = 8 is the root of (1/2)x + 7 = 11 
 
Solution: 
(i) Given x = 4 is the root of 3x - 5 = 7 
Now, substituting x = 4 in place of ‘x’ in the given equation, we get 
= 3(4) – 5 = 7 
= 12 – 5 = 7 
7 = 7 
Since, LHS = RHS 
Hence, x = 4 is the root of 3x - 5 = 7. 
 
(ii) Given x = 3 is the root of 5 + 3x = 14. 
Now, substituting x = 3 in place of ‘x’ in the given equation, we get 
= 5 + 3(3) = 14 
= 5 + 9 = 14 
14 = 14 
Since, LHS = RHS 
Hence, x = 3 is the root of 5 + 3x = 14. 
 
(iii) Given x = 2 is the root of 3x – 2 = 8x – 12. 
Now, substituting x = 2 in place of ‘x’ in the given equation, we get 
= 3(2) – 2 = 8(2) – 12 
= 6 – 2 = 16 – 12 
4 = 4 
Since, LHS = RHS 
Hence, x = 2 is the root of 3x – 2 = 8x – 12. 
 
(iv) Given x = 4 is the root of 3x/2 = 6. 
 
  
Now, substituting x = 4 in place of ‘x’ in the given equation, we get 
= (3 × 4)/2 = 6 
= (12/2) = 6 
6 = 6 
Since, LHS = RHS 
Hence, x = 4 is the root of (3x/2) = 6. 
(v) Given y = 2 is the root of y – 3 = 2y – 5.
Now, substituting y = 2 in place of ‘y’ in the given equation, we get
= 2 – 3 = 2(2) – 5
= -1 = 4 – 5
-1 = -1
Since, LHS = RHS
Hence, y = 2 is the root of y – 3 = 2y – 5.
(vi) Given x = 8 is the root of (1/2)x + 7 = 11.
Now, substituting x = 8 in place of ‘x’ in the given equation, we get
= (1/2)(8) + 7 =11
= 4 + 7 = 11
= 11 = 11
Since, LHS = RHS
Hence, x = 8 is the root of 12x + 7 = 11.
2. Solve each of the following equations by trial – and – error method:
(i) x + 3 =12
(ii) x -7 = 10
(iii) 4x = 28
(iv) (x/2) + 7 = 11
(v) 2x + 4 = 3x
(vi) (x/4) = 12
(vii) (15/x) = 3
(vii) (x/18) = 20
Solution: 
(i) Given x + 3 =12
Here LHS = x +3 and RHS = 12
Page 3


 
 
 
 
 
 
 
Exercise 8.1        Page No: 8.6 
 
1. Verify by substitution that: 
(i) x = 4 is the root of 3x – 5 = 7 
(ii) x = 3 is the root of 5 + 3x = 14 
(iii) x = 2 is the root of 3x – 2 = 8x – 12 
(iv) x = 4 is the root of (3x/2) = 6 
(v) y = 2 is the root of y – 3 = 2y – 5 
(vi) x = 8 is the root of (1/2)x + 7 = 11 
 
Solution: 
(i) Given x = 4 is the root of 3x - 5 = 7 
Now, substituting x = 4 in place of ‘x’ in the given equation, we get 
= 3(4) – 5 = 7 
= 12 – 5 = 7 
7 = 7 
Since, LHS = RHS 
Hence, x = 4 is the root of 3x - 5 = 7. 
 
(ii) Given x = 3 is the root of 5 + 3x = 14. 
Now, substituting x = 3 in place of ‘x’ in the given equation, we get 
= 5 + 3(3) = 14 
= 5 + 9 = 14 
14 = 14 
Since, LHS = RHS 
Hence, x = 3 is the root of 5 + 3x = 14. 
 
(iii) Given x = 2 is the root of 3x – 2 = 8x – 12. 
Now, substituting x = 2 in place of ‘x’ in the given equation, we get 
= 3(2) – 2 = 8(2) – 12 
= 6 – 2 = 16 – 12 
4 = 4 
Since, LHS = RHS 
Hence, x = 2 is the root of 3x – 2 = 8x – 12. 
 
(iv) Given x = 4 is the root of 3x/2 = 6. 
 
  
Now, substituting x = 4 in place of ‘x’ in the given equation, we get 
= (3 × 4)/2 = 6 
= (12/2) = 6 
6 = 6 
Since, LHS = RHS 
Hence, x = 4 is the root of (3x/2) = 6. 
(v) Given y = 2 is the root of y – 3 = 2y – 5.
Now, substituting y = 2 in place of ‘y’ in the given equation, we get
= 2 – 3 = 2(2) – 5
= -1 = 4 – 5
-1 = -1
Since, LHS = RHS
Hence, y = 2 is the root of y – 3 = 2y – 5.
(vi) Given x = 8 is the root of (1/2)x + 7 = 11.
Now, substituting x = 8 in place of ‘x’ in the given equation, we get
= (1/2)(8) + 7 =11
= 4 + 7 = 11
= 11 = 11
Since, LHS = RHS
Hence, x = 8 is the root of 12x + 7 = 11.
2. Solve each of the following equations by trial – and – error method:
(i) x + 3 =12
(ii) x -7 = 10
(iii) 4x = 28
(iv) (x/2) + 7 = 11
(v) 2x + 4 = 3x
(vi) (x/4) = 12
(vii) (15/x) = 3
(vii) (x/18) = 20
Solution: 
(i) Given x + 3 =12
Here LHS = x +3 and RHS = 12
 
 
 
 
 
 
 
x LHS RHS Is LHS = RHS 
1 1 + 3 = 4 12 No 
2 2 + 3 = 5 12 No 
3 3 + 3 = 6 12 No 
4 4 + 3 = 7 12 No 
5 5 + 3 = 8 12 No 
6 6 + 3 = 9 12 No 
7 7 + 3 = 10 12 No 
8 8 + 3 = 11 12 No 
9 9 + 3 = 12 12 Yes 
 
Therefore, if x = 9, LHS = RHS. 
Hence, x = 9 is the solution to this equation. 
 
(ii) Given x -7 = 10 
Here LHS = x -7 and RHS = 10 
x LHS RHS Is LHS = RHS 
9 9 – 7 = 2 10 No 
10 10 -7 = 3 10 No 
11 11 – 7 = 4 10 No 
12 12 – 7 = 5 10 No 
13 19 – 7 = 6 10 No 
14 14 – 7 = 7 10 No 
15 15 – 7 = 8 10 No 
16 16 – 7 = 9 10 No 
17 17 – 7 = 10 10 Yes 
 
Therefore if x = 17, LHS = RHS 
Hence, x = 17 is the solution to this equation. 
 
(iii) Given 4x = 28 
Here LHS = 4x and RHS = 28 
 
 
 
 
Page 4


 
 
 
 
 
 
 
Exercise 8.1        Page No: 8.6 
 
1. Verify by substitution that: 
(i) x = 4 is the root of 3x – 5 = 7 
(ii) x = 3 is the root of 5 + 3x = 14 
(iii) x = 2 is the root of 3x – 2 = 8x – 12 
(iv) x = 4 is the root of (3x/2) = 6 
(v) y = 2 is the root of y – 3 = 2y – 5 
(vi) x = 8 is the root of (1/2)x + 7 = 11 
 
Solution: 
(i) Given x = 4 is the root of 3x - 5 = 7 
Now, substituting x = 4 in place of ‘x’ in the given equation, we get 
= 3(4) – 5 = 7 
= 12 – 5 = 7 
7 = 7 
Since, LHS = RHS 
Hence, x = 4 is the root of 3x - 5 = 7. 
 
(ii) Given x = 3 is the root of 5 + 3x = 14. 
Now, substituting x = 3 in place of ‘x’ in the given equation, we get 
= 5 + 3(3) = 14 
= 5 + 9 = 14 
14 = 14 
Since, LHS = RHS 
Hence, x = 3 is the root of 5 + 3x = 14. 
 
(iii) Given x = 2 is the root of 3x – 2 = 8x – 12. 
Now, substituting x = 2 in place of ‘x’ in the given equation, we get 
= 3(2) – 2 = 8(2) – 12 
= 6 – 2 = 16 – 12 
4 = 4 
Since, LHS = RHS 
Hence, x = 2 is the root of 3x – 2 = 8x – 12. 
 
(iv) Given x = 4 is the root of 3x/2 = 6. 
 
  
Now, substituting x = 4 in place of ‘x’ in the given equation, we get 
= (3 × 4)/2 = 6 
= (12/2) = 6 
6 = 6 
Since, LHS = RHS 
Hence, x = 4 is the root of (3x/2) = 6. 
(v) Given y = 2 is the root of y – 3 = 2y – 5.
Now, substituting y = 2 in place of ‘y’ in the given equation, we get
= 2 – 3 = 2(2) – 5
= -1 = 4 – 5
-1 = -1
Since, LHS = RHS
Hence, y = 2 is the root of y – 3 = 2y – 5.
(vi) Given x = 8 is the root of (1/2)x + 7 = 11.
Now, substituting x = 8 in place of ‘x’ in the given equation, we get
= (1/2)(8) + 7 =11
= 4 + 7 = 11
= 11 = 11
Since, LHS = RHS
Hence, x = 8 is the root of 12x + 7 = 11.
2. Solve each of the following equations by trial – and – error method:
(i) x + 3 =12
(ii) x -7 = 10
(iii) 4x = 28
(iv) (x/2) + 7 = 11
(v) 2x + 4 = 3x
(vi) (x/4) = 12
(vii) (15/x) = 3
(vii) (x/18) = 20
Solution: 
(i) Given x + 3 =12
Here LHS = x +3 and RHS = 12
 
 
 
 
 
 
 
x LHS RHS Is LHS = RHS 
1 1 + 3 = 4 12 No 
2 2 + 3 = 5 12 No 
3 3 + 3 = 6 12 No 
4 4 + 3 = 7 12 No 
5 5 + 3 = 8 12 No 
6 6 + 3 = 9 12 No 
7 7 + 3 = 10 12 No 
8 8 + 3 = 11 12 No 
9 9 + 3 = 12 12 Yes 
 
Therefore, if x = 9, LHS = RHS. 
Hence, x = 9 is the solution to this equation. 
 
(ii) Given x -7 = 10 
Here LHS = x -7 and RHS = 10 
x LHS RHS Is LHS = RHS 
9 9 – 7 = 2 10 No 
10 10 -7 = 3 10 No 
11 11 – 7 = 4 10 No 
12 12 – 7 = 5 10 No 
13 19 – 7 = 6 10 No 
14 14 – 7 = 7 10 No 
15 15 – 7 = 8 10 No 
16 16 – 7 = 9 10 No 
17 17 – 7 = 10 10 Yes 
 
Therefore if x = 17, LHS = RHS 
Hence, x = 17 is the solution to this equation. 
 
(iii) Given 4x = 28 
Here LHS = 4x and RHS = 28 
 
 
 
 
 
 
 
 
 
 
 
x LHS RHS Is LHS = RHS 
1 4 × 1 = 4 28 No 
2 4 × 2 = 8 28 No 
3 4 × 3 = 12 28 No 
4 4 × 4 = 16 28 No 
5 4 × 5 = 20 28 No 
6 4 × 6 = 24 28 No 
7 4 × 7 = 28 28 Yes 
 
Therefore if x = 7, LHS = RHS 
Hence, x = 7 is the solution to this equation. 
 
(iv) Given (x/2) + 7 = 11 
Here LHS = (x/2) + 7 and RHS = 11 
Since RHS is a natural number, (x/2) must also be a natural number, so we must 
substitute values of x that are multiples of 2. 
x LHS RHS Is LHS = RHS 
2 (2/2) + 7 = 1 + 7  =8 11 No 
4 (4/2) + 7 = 2 + 7 = 9 11 No 
6 (6/2) + 7 = 3 + 7 = 10 11 No 
8 (8/2) + 7 = 4 + 7 = 11 11 Yes 
 
Therefore if x = 8, LHS = RHS 
Hence, x = 8 is the solutions to this equation. 
 
(v) Given 2x + 4 = 3x 
Here LHS = 2x + 4 and RHS = 3x 
x LHS RHS Is LHS = RHS 
1 2 (1) + 4 = 2 + 4 = 6 3 (1) = 3 No 
2 2 (2) + 4 = 4 + 4 = 8 3 (2) = 6 No 
3 2 (3) + 4 = 6 + 4 = 10 3 (3) = 9 No 
4 2 (4) + 4 = 8 + 4 = 12 3 (4) = 12 Yes 
 
Therefore if x = 4, LHS = RHS 
Hence, x = 4 is the solutions to this equation. 
 
Page 5


 
 
 
 
 
 
 
Exercise 8.1        Page No: 8.6 
 
1. Verify by substitution that: 
(i) x = 4 is the root of 3x – 5 = 7 
(ii) x = 3 is the root of 5 + 3x = 14 
(iii) x = 2 is the root of 3x – 2 = 8x – 12 
(iv) x = 4 is the root of (3x/2) = 6 
(v) y = 2 is the root of y – 3 = 2y – 5 
(vi) x = 8 is the root of (1/2)x + 7 = 11 
 
Solution: 
(i) Given x = 4 is the root of 3x - 5 = 7 
Now, substituting x = 4 in place of ‘x’ in the given equation, we get 
= 3(4) – 5 = 7 
= 12 – 5 = 7 
7 = 7 
Since, LHS = RHS 
Hence, x = 4 is the root of 3x - 5 = 7. 
 
(ii) Given x = 3 is the root of 5 + 3x = 14. 
Now, substituting x = 3 in place of ‘x’ in the given equation, we get 
= 5 + 3(3) = 14 
= 5 + 9 = 14 
14 = 14 
Since, LHS = RHS 
Hence, x = 3 is the root of 5 + 3x = 14. 
 
(iii) Given x = 2 is the root of 3x – 2 = 8x – 12. 
Now, substituting x = 2 in place of ‘x’ in the given equation, we get 
= 3(2) – 2 = 8(2) – 12 
= 6 – 2 = 16 – 12 
4 = 4 
Since, LHS = RHS 
Hence, x = 2 is the root of 3x – 2 = 8x – 12. 
 
(iv) Given x = 4 is the root of 3x/2 = 6. 
 
  
Now, substituting x = 4 in place of ‘x’ in the given equation, we get 
= (3 × 4)/2 = 6 
= (12/2) = 6 
6 = 6 
Since, LHS = RHS 
Hence, x = 4 is the root of (3x/2) = 6. 
(v) Given y = 2 is the root of y – 3 = 2y – 5.
Now, substituting y = 2 in place of ‘y’ in the given equation, we get
= 2 – 3 = 2(2) – 5
= -1 = 4 – 5
-1 = -1
Since, LHS = RHS
Hence, y = 2 is the root of y – 3 = 2y – 5.
(vi) Given x = 8 is the root of (1/2)x + 7 = 11.
Now, substituting x = 8 in place of ‘x’ in the given equation, we get
= (1/2)(8) + 7 =11
= 4 + 7 = 11
= 11 = 11
Since, LHS = RHS
Hence, x = 8 is the root of 12x + 7 = 11.
2. Solve each of the following equations by trial – and – error method:
(i) x + 3 =12
(ii) x -7 = 10
(iii) 4x = 28
(iv) (x/2) + 7 = 11
(v) 2x + 4 = 3x
(vi) (x/4) = 12
(vii) (15/x) = 3
(vii) (x/18) = 20
Solution: 
(i) Given x + 3 =12
Here LHS = x +3 and RHS = 12
 
 
 
 
 
 
 
x LHS RHS Is LHS = RHS 
1 1 + 3 = 4 12 No 
2 2 + 3 = 5 12 No 
3 3 + 3 = 6 12 No 
4 4 + 3 = 7 12 No 
5 5 + 3 = 8 12 No 
6 6 + 3 = 9 12 No 
7 7 + 3 = 10 12 No 
8 8 + 3 = 11 12 No 
9 9 + 3 = 12 12 Yes 
 
Therefore, if x = 9, LHS = RHS. 
Hence, x = 9 is the solution to this equation. 
 
(ii) Given x -7 = 10 
Here LHS = x -7 and RHS = 10 
x LHS RHS Is LHS = RHS 
9 9 – 7 = 2 10 No 
10 10 -7 = 3 10 No 
11 11 – 7 = 4 10 No 
12 12 – 7 = 5 10 No 
13 19 – 7 = 6 10 No 
14 14 – 7 = 7 10 No 
15 15 – 7 = 8 10 No 
16 16 – 7 = 9 10 No 
17 17 – 7 = 10 10 Yes 
 
Therefore if x = 17, LHS = RHS 
Hence, x = 17 is the solution to this equation. 
 
(iii) Given 4x = 28 
Here LHS = 4x and RHS = 28 
 
 
 
 
 
 
 
 
 
 
 
x LHS RHS Is LHS = RHS 
1 4 × 1 = 4 28 No 
2 4 × 2 = 8 28 No 
3 4 × 3 = 12 28 No 
4 4 × 4 = 16 28 No 
5 4 × 5 = 20 28 No 
6 4 × 6 = 24 28 No 
7 4 × 7 = 28 28 Yes 
 
Therefore if x = 7, LHS = RHS 
Hence, x = 7 is the solution to this equation. 
 
(iv) Given (x/2) + 7 = 11 
Here LHS = (x/2) + 7 and RHS = 11 
Since RHS is a natural number, (x/2) must also be a natural number, so we must 
substitute values of x that are multiples of 2. 
x LHS RHS Is LHS = RHS 
2 (2/2) + 7 = 1 + 7  =8 11 No 
4 (4/2) + 7 = 2 + 7 = 9 11 No 
6 (6/2) + 7 = 3 + 7 = 10 11 No 
8 (8/2) + 7 = 4 + 7 = 11 11 Yes 
 
Therefore if x = 8, LHS = RHS 
Hence, x = 8 is the solutions to this equation. 
 
(v) Given 2x + 4 = 3x 
Here LHS = 2x + 4 and RHS = 3x 
x LHS RHS Is LHS = RHS 
1 2 (1) + 4 = 2 + 4 = 6 3 (1) = 3 No 
2 2 (2) + 4 = 4 + 4 = 8 3 (2) = 6 No 
3 2 (3) + 4 = 6 + 4 = 10 3 (3) = 9 No 
4 2 (4) + 4 = 8 + 4 = 12 3 (4) = 12 Yes 
 
Therefore if x = 4, LHS = RHS 
Hence, x = 4 is the solutions to this equation. 
 
 
 
 
 
 
 
 
(vi) Given (x/4) = 12 
Here LHS = (x/4) and RHS = 12 
Since RHS is a natural number, x/4 must also be a natural number, so we must 
substitute values of x that are multiples of 4. 
x LHS RHS Is LHS = RHS 
16 (16/4) = 4 12 No 
20 (20/4) = 5 12 No 
24 (24/4) = 6 12 No 
28 (28/4) = 7 12 No 
32 (32/4) = 8 12 No 
36 (36/4) = 9 12 No 
40 (40/4) = 10 12 No 
44 (44/4) = 11 12 No 
48 (48/4) = 12 12 Yes 
 
Therefore if x = 48, LHS = RHS 
Hence, x = 48 is the solutions to this equation. 
 
(vii) Given (15/x) = 3 
Here LHS = (15/x) and RHS = 3 
Since RHS is a natural number, 15x must also be a natural number, so we must 
substitute values of x that are factors of 15. 
x LHS RHS Is LHS = RHS 
1 (15/1) = 15 3 No 
3 (15/3) = 5 3 No 
5 (15/5) = 3 3 Yes 
 
 
Therefore if x = 5, LHS = RHS 
Hence, x = 5 is the solutions to this equation. 
 
(viii) Given (x/18) = 20 
Here LHS = (x/18) and RHS = 20 
Since RHS is a natural number, (x/18) must also be a natural number, so we must 
substitute values of x that are multiples of 18. 
 
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FAQs on Linear Equations in One Variable (Exercise 8.1) RD Sharma Solutions - Mathematics (Maths) Class 7

1. How do you solve linear equations in one variable?
Ans. To solve a linear equation in one variable, you need to isolate the variable term on one side of the equation. You can do this by using properties of equality and performing inverse operations. The goal is to simplify the equation until you have the variable term alone on one side and the constant term on the other side.
2. What are the steps to solve a linear equation in one variable?
Ans. The steps to solve a linear equation in one variable are as follows: 1. Simplify both sides of the equation by combining like terms. 2. Isolate the variable term on one side of the equation by performing inverse operations. 3. Simplify further if needed by combining like terms again. 4. Check the solution by substituting it back into the original equation to ensure that it satisfies the equation.
3. Can a linear equation have more than one solution?
Ans. Yes, a linear equation can have more than one solution. This happens when both sides of the equation are equal for any value of the variable. In such cases, the variable can take on any value and still satisfy the equation. These types of equations are called identity equations and have infinitely many solutions.
4. Can a linear equation have no solution?
Ans. Yes, a linear equation can have no solution. This occurs when the equation leads to a contradiction, meaning that there is no value of the variable that satisfies the equation. For example, if you end up with an equation like 2 = 3, there is no value of the variable that can make this equation true. These types of equations are called inconsistent equations.
5. Can a linear equation in one variable have a fraction as its solution?
Ans. Yes, a linear equation in one variable can have a fraction as its solution. The solution can be in the form of a fraction if the equation involves dividing or multiplying by a non-zero number. When solving such equations, you should perform all operations to isolate the variable term, even if it involves fractions.
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