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NCERT Solutions for Class 12 Math Chapter 4 – Determinants

January 19, 2021 by SSCGuides Leave a Comment

The topics and sub-topics included in the Determinants chapter are the following:

Section NameTopic Name
4Determinants
4.1Introduction
4.2Determinant
4.3Properties of Determinants
4.4Area of a Triangle
4.5Adjoint and Inverse of a Matrix
4.6Applications of Determinants and Matrices
4.7Summary

More Resources for CBSE Class 12

  • NCERT Solutions for Class 12 (All Chapter)
  • NCERT Solutions for Class 12 Physics
  • NCERT Solutions for Class 12 Chemistry
  • NCERT Solutions for Class 12 Math
  • NCERT Solutions for Class 12 Biology
  • NCERT Solutions for Class 12 Economics
  • NCERT Solutions for Class 12 English
Contents show
1 Class 12 Maths NCERT Solutions Chapter 4 Determinants
1.1 Page No 108:
1.2 Question 1:
1.3 Answer:
1.4 Question 2:
1.5 Answer:
1.6 Question 3:
1.7 Answer:
1.8 Question 4:
1.9 Answer:
1.10 Question 5:
1.11 Answer:
1.12 Page No 109:
1.13 Question 6:
1.14 Answer:
1.15 Question 7:
1.16 Answer:
1.17 Question 8:
1.18 Answer:
1.19 Page No 119:
1.20 Question 1:
1.21 Answer:
1.22 Question 2:
1.23 Answer:
1.24 Question 3:
1.25 Answer:
1.26 Question 4:
1.27 Answer:
1.28 Question 5:
1.29 Answer:
1.30 Page No 120:
1.31 Question 6:
1.32 Answer:
1.33 Question 7:
1.34 Answer:
1.35 Question 8:
1.36 Answer:
1.37 Question 9:
1.38 Answer:
1.39 Question 10:
1.40 Answer:
1.41 Question 11:
1.42 Answer:
1.43 Page No 121:
1.44 Question 12:
1.45 Answer:
1.46 Question 13:
1.47 Answer:
1.48 Question 14:
1.49 Answer:
1.50 Question 15:
1.51 Answer:
1.52 Question 16:
1.53 Answer:
1.54 Page No 122:
1.55 Question 1:
1.56 Answer:
1.57 Page No 123:
1.58 Question 2:
1.59 Answer:
1.60 Question 3:
1.61 Answer:
1.62 Question 4:
1.63 Answer:
1.64 Question 5:
1.65 Answer:
1.66 Page No 126:
1.67 Question 1:
1.68 Answer:
1.69 Question 2:
1.70 Answer:
1.71 Question 3:
1.72 Answer:
1.73 Question 4:
1.74 Answer:
1.75 Question 5:
1.76 Answer:
1.77 Page No 131:
1.78 Question 1:
1.79 Answer:
1.80 Question 2:
1.81 Answer:
1.82 Question 3:
1.83 Answer:
1.84 Question 4:
1.85 Answer:
1.86 Page No 132:
1.87 Question 5:
1.88 Answer:
1.89 Question 6:
1.90 Answer:
1.91 Question 7:
1.92 Answer:
1.93 Question 8:
1.94 Answer:
1.95 Question 9:
1.96 Answer:
1.97 Question 10:
1.98 Answer:
1.99 Question 11:
1.100 Answer:
1.101 Question 12:
1.102 Answer:
1.103 Question 13:
1.104 Answer:
1.105 Question 14:
1.106 Answer:
1.107 Question 15:
1.108 Answer:
1.109 Question 16:
1.110 Answer:
1.111 Question 17:
1.112 Answer:
1.113 Question 18:
1.114 Answer:
1.115 Page No 136:
1.116 Question 1:
1.117 Answer:
1.118 Question 2:
1.119 Answer:
1.120 Question 3:
1.121 Answer:
1.122 Question 4:
1.123 Answer:
1.124 Question 5:
1.125 Answer:
1.126 Question 6:
1.127 Answer:
1.128 Question 7:
1.129 Answer:
1.130 Question 8:
1.131 Answer:
1.132 Question 9:
1.133 Answer:
1.134 Question 10:
1.135 Answer:
1.136 Question 11:
1.137 Answer:
1.138 Question 12:
1.139 Answer:
1.140 Question 13:
1.141 Answer:
1.142 Question 14:
1.143 Answer:
1.144 Page No 137:
1.145 Question 15:
1.146 Answer:
1.147 Question 16:
1.148 Answer:
1.149 Page No 141:
1.150 Question 1:
1.151 Answer:
1.152 Question 2:
1.153 Answer:
1.154 Question 3:
1.155 Answer:
1.156 Question 4:
1.157 Answer:
1.158 Question 5:
1.159 Answer:
1.160 Question 6:
1.161 Answer:
1.162 Question 7:
1.163 Answer:
1.164 Page No 142:
1.165 Question 8:
1.166 Answer:
1.167 Question 9:
1.168 Answer:
1.169 Question 10:
1.170 Answer:
1.171 Question 11:
1.172 Answer:
1.173 Question 12:
1.174 Answer:
1.175 Question 13:
1.176 Answer:
1.177 Question 14:
1.178 Answer:
1.179 Question 15:
1.180 Answer:
1.181 Question 16:
1.182 Answer:
1.183 Page No 143:
1.184 Question 17:
1.185 Answer:
1.186 Question 18:
1.187 Answer:
1.188 Question 19:
1.189 Answer:
2 NCERT Solutions for Class 12 Maths

Class 12 Maths NCERT Solutions Chapter 4 Determinants


Page No 108:

Question 1:

Evaluate the determinants in Exercises 1 and 2.

Answer:

 = 2(−1) − 4(−5) = − 2 + 20 = 18


Question 2:

Evaluate the determinants in Exercises 1 and 2.

(i)  (ii) 

Answer:

(i)  = (cos θ)(cos θ) − (−sin θ)(sin θ) = cos2 θ+ sin2 θ = 1

(ii) 

= (x2 − x + 1)(x + 1) − (x − 1)(x + 1)

= x3 − x2 + x + x2 − x + 1 − (x2 − 1)

= x3 + 1 − x2 + 1

= x3 − x2 + 2


Question 3:

If, then show that

Answer:

The given matrix is.


Question 4:

If, then show that

Answer:

The given matrix is.

It can be observed that in the first column, two entries are zero. Thus, we expand along the first column (C1) for easier calculation.

From equations (i) and (ii), we have:

Hence, the given result is proved.


Question 5:

Evaluate the determinants

(i)  (iii) 

(ii)  (iv) 

Answer:

(i) Let.

It can be observed that in the second row, two entries are zero. Thus, we expand along the second row for easier calculation.

(ii) Let.

By expanding along the first row, we have:

(iii) Let

By expanding along the first row, we have:

(iv) Let

By expanding along the first column, we have:

Page No 109:

Question 6:

If, find.

Answer:

Let

By expanding along the first row, we have:

Question 7:

Find values of x, if

(i)

2451=2x46x(ii)

2345=x32x5

Answer:

(i) 

(ii) 

Question 8:

If, then x is equal to

(A) 6 (B) ±6 (C) −6 (D) 0

Answer:

Answer: B

Hence, the correct answer is B.

Page No 119:

Question 1:

Using the property of determinants and without expanding, prove that:

Answer:

Question 2:

Using the property of determinants and without expanding, prove that:

Answer:

Here, the two rows R1 and R3 are identical.

Δ = 0.

Question 3:

Using the property of determinants and without expanding, prove that:

Answer:

Question 4:

Using the property of determinants and without expanding, prove that:

Answer:

By applying C3 → C3 + C2, we have:

Here, two columns C1 and C3 are proportional.

Δ = 0.

Question 5:

Using the property of determinants and without expanding, prove that:

Answer:

Applying R2 → R2 − R3, we have:

Applying R1 ↔R3 and R2 ↔R3, we have:

Applying R1 → R1 − R3, we have:

Applying R1 ↔R2 and R2 ↔R3, we have:

From (1), (2), and (3), we have:

Hence, the given result is proved.

Page No 120:

Question 6:

By using properties of determinants, show that:

Answer:

We have,

Here, the two rows R1 and R3 are identical.

∴Δ = 0.

Question 7:

By using properties of determinants, show that:

Answer:

Applying R2 → R2 + R1 and R3 → R3 + R1, we have:

Question 8:

By using properties of determinants, show that:

(i) 

(ii) 

Answer:

(i) 

Applying R1 → R1 − R3 and R2 → R2 − R3, we have:

Applying R1 → R1 + R2, we have:

Expanding along C1, we have:

Hence, the given result is proved.

(ii) Let.

Applying C1 → C1 − C3 and C2 → C2 − C3, we have:

Applying C1 → C1 + C2, we have:

Expanding along C1, we have:

Hence, the given result is proved.

Question 9:

By using properties of determinants, show that:

Answer:

Applying R2 → R2 − R1 and R3 → R3 − R1, we have:

Applying R3 → R3 + R2, we have:

Expanding along R3, we have:

Hence, the given result is proved.

Question 10:

By using properties of determinants, show that:

(i) 

(ii) 

Answer:

(i) 

Applying R1 → R1 + R2 + R3, we have:

Applying C2 → C2 − C1, C3 → C3 − C1, we have:

Expanding along C3, we have:

Hence, the given result is proved.

(ii) 

Applying R1 → R1 + R2 + R3, we have:

Applying C2 → C2 − C1 and C3 → C3 − C1, we have:

Expanding along C3, we have:

Hence, the given result is proved.

Question 11:

By using properties of determinants, show that:

(i) 

(ii) 

Answer:

(i) 

Applying R1 → R1 + R2 + R3, we have:

Applying C2 → C2 − C1, C3 → C3 − C1, we have:

Expanding along C3, we have:

Hence, the given result is proved.

(ii) 

Applying C1 → C1 + C2 + C3, we have:

Applying R2 → R2 − R1 and R3 → R3 − R1, we have:

Expanding along R3, we have:

Hence, the given result is proved.

Page No 121:

Question 12:

By using properties of determinants, show that:

Answer:

Applying R1 → R1 + R2 + R3, we have:

Applying C2 → C2 − C1 and C3 → C3 − C1, we have:

Expanding along R1, we have:

Hence, the given result is proved.

Question 13:

By using properties of determinants, show that:

Answer:

Applying R1 → R1 + bR3 and R2 → R2 − aR3, we have:

Expanding along R1, we have:

Question 14:

By using properties of determinants, show that:

Answer:

Taking out common factors a, b, and c from R1, R2, and R3 respectively, we have:

Applying R2 → R2 − R1 and R3 → R3 − R1, we have:

Applying C1 → aC1, C2 → bC2, and C3 → cC3, we have:

Expanding along R3, we have:

Hence, the given result is proved.

Question 15:

Choose the correct answer.

Let A be a square matrix of order 3 × 3, then is equal to

A.  B.  C.  D.

Answer:

Answer: C

A is a square matrix of order 3 × 3.

Hence, the correct answer is C.

Question 16:

Which of the following is correct?

A. Determinant is a square matrix.

B. Determinant is a number associated to a matrix.

C. Determinant is a number associated to a square matrix.

D. None of these

Answer:

Answer: C

We know that to every square matrix, of order n. We can associate a number called the determinant of square matrix A, where element of A.

Thus, the determinant is a number associated to a square matrix.

Hence, the correct answer is C.

Page No 122:

Question 1:

Find area of the triangle with vertices at the point given in each of the following:

(i) (1, 0), (6, 0), (4, 3) (ii) (2, 7), (1, 1), (10, 8)

(iii) (−2, −3), (3, 2), (−1, −8)

Answer:

(i) The area of the triangle with vertices (1, 0), (6, 0), (4, 3) is given by the relation,

(ii) The area of the triangle with vertices (2, 7), (1, 1), (10, 8) is given by the relation,

(iii) The area of the triangle with vertices (−2, −3), (3, 2), (−1, −8)

is given by the relation,

Hence, the area of the triangle is.

Page No 123:

Question 2:

Show that points

are collinear

Answer:

Area of ΔABC is given by the relation,

Thus, the area of the triangle formed by points A, B, and C is zero.

Hence, the points A, B, and C are collinear.

Question 3:

Find values of k if area of triangle is 4 square units and vertices are

(i) (k, 0), (4, 0), (0, 2) (ii) (−2, 0), (0, 4), (0, k)

Answer:

We know that the area of a triangle whose vertices are (x1, y1), (x2, y2), and

(x3, y3) is the absolute value of the determinant (Δ), where

It is given that the area of triangle is 4 square units.

∴Δ = ± 4.

(i) The area of the triangle with vertices (k, 0), (4, 0), (0, 2) is given by the relation,

Δ =

∴−k + 4 = ± 4

When −k + 4 = − 4, k = 8.

When −k + 4 = 4, k = 0.

Hence, k = 0, 8.

(ii) The area of the triangle with vertices (−2, 0), (0, 4), (0, k) is given by the relation,

Δ =

∴k − 4 = ± 4

When k − 4 = − 4, k = 0.

When k − 4 = 4, k = 8.

Hence, k = 0, 8.

Question 4:

(i) Find equation of line joining (1, 2) and (3, 6) using determinants

(ii) Find equation of line joining (3, 1) and (9, 3) using determinants

Answer:

(i) Let P (x, y) be any point on the line joining points A (1, 2) and B (3, 6). Then, the points A, B, and P are collinear. Therefore, the area of triangle ABP will be zero.

Hence, the equation of the line joining the given points is y = 2x.

(ii) Let P (x, y) be any point on the line joining points A (3, 1) and

B (9, 3). Then, the points A, B, and P are collinear. Therefore, the area of triangle ABP will be zero.

Hence, the equation of the line joining the given points is x − 3y = 0.

Question 5:

If area of triangle is 35 square units with vertices (2, −6), (5, 4), and (k, 4). Then k is

A. 12 B. −2 C. −12, −2 D. 12, −2

Answer:

Answer: D

The area of the triangle with vertices (2, −6), (5, 4), and (k, 4) is given by the relation,

It is given that the area of the triangle is ±35.

Therefore, we have:

When 5 − k = −7, k = 5 + 7 = 12.

When 5 − k = 7, k = 5 − 7 = −2.

Hence, k = 12, −2.

The correct answer is D.

Page No 126:

Question 1:

Write Minors and Cofactors of the elements of following determinants:

(i)  (ii) 

Answer:

(i) The given determinant is.

Minor of element aij is Mij.

∴M11 = minor of element a11 = 3

M12 = minor of element a12 = 0

M21 = minor of element a21 = −4

M22 = minor of element a22 = 2

Cofactor of aij is Aij = (−1)i + j Mij.

∴A11 = (−1)1+1 M11 = (−1)2 (3) = 3

A12 = (−1)1+2 M12 = (−1)3 (0) = 0

A21 = (−1)2+1 M21 = (−1)3 (−4) = 4

A22 = (−1)2+2 M22 = (−1)4 (2) = 2

(ii) The given determinant is.

Minor of element aij is Mij.

∴M11 = minor of element a11 = d

M12 = minor of element a12 = b

M21 = minor of element a21 = c

M22 = minor of element a22 = a

Cofactor of aij is Aij = (−1)i + j Mij.

∴A11 = (−1)1+1 M11 = (−1)2 (d) = d

A12 = (−1)1+2 M12 = (−1)3 (b) = −b

A21 = (−1)2+1 M21 = (−1)3 (c) = −c

A22 = (−1)2+2 M22 = (−1)4 (a) = a

Question 2:

(i)  (ii) 

Answer:

(i) The given determinant is.

By the definition of minors and cofactors, we have:

M11 = minor of a11= 

M12 = minor of a12= 

M13 = minor of a13 = 

M21 = minor of a21 = 

M22 = minor of a22 = 

M23 = minor of a23 = 

M31 = minor of a31= 

M32 = minor of a32 = 

M33 = minor of a33 = 

A11 = cofactor of a11= (−1)1+1 M11 = 1

A12 = cofactor of a12 = (−1)1+2 M12 = 0

A13 = cofactor of a13 = (−1)1+3 M13 = 0

A21 = cofactor of a21 = (−1)2+1 M21 = 0

A22 = cofactor of a22 = (−1)2+2 M22 = 1

A23 = cofactor of a23 = (−1)2+3 M23 = 0

A31 = cofactor of a31 = (−1)3+1 M31 = 0

A32 = cofactor of a32 = (−1)3+2 M32 = 0

A33 = cofactor of a33 = (−1)3+3 M33 = 1

(ii) The given determinant is.

By definition of minors and cofactors, we have:

M11 = minor of a11= 

M12 = minor of a12= 

M13 = minor of a13 = 

M21 = minor of a21 = 

M22 = minor of a22 = 

M23 = minor of a23 = 

M31 = minor of a31= 

M32 = minor of a32 = 

M33 = minor of a33 = 

A11 = cofactor of a11= (−1)1+1 M11 = 11

A12 = cofactor of a12 = (−1)1+2 M12 = −6

A13 = cofactor of a13 = (−1)1+3 M13 = 3

A21 = cofactor of a21 = (−1)2+1 M21 = 4

A22 = cofactor of a22 = (−1)2+2 M22 = 2

A23 = cofactor of a23 = (−1)2+3 M23 = −1

A31 = cofactor of a31 = (−1)3+1 M31 = −20

A32 = cofactor of a32 = (−1)3+2 M32 = 13

A33 = cofactor of a33 = (−1)3+3 M33 = 5

Question 3:

Using Cofactors of elements of second row, evaluate.

Answer:

The given determinant is.

We have:

M21 = 

∴A21 = cofactor of a21 = (−1)2+1 M21 = 7

M22 = 

∴A22 = cofactor of a22 = (−1)2+2 M22 = 7

M23 = 

∴A23 = cofactor of a23 = (−1)2+3 M23 = −7

We know that Δ is equal to the sum of the product of the elements of the second row with their corresponding cofactors.

∴Δ = a21A21 + a22A22 + a23A23 = 2(7) + 0(7) + 1(−7) = 14 − 7 = 7

Question 4:

Using Cofactors of elements of third column, evaluate

Answer:

The given determinant is.

We have:

M13 = 

M23 = 

M33 = 

∴A13 = cofactor of a13 = (−1)1+3 M13 = (z − y)

A23 = cofactor of a23 = (−1)2+3 M23 = − (z − x) = (x − z)

A33 = cofactor of a33 = (−1)3+3 M33 = (y − x)

We know that Δ is equal to the sum of the product of the elements of the second row with their corresponding cofactors.

Hence, 

Question 5:

If  and Aij is Cofactors of aij, then value of Δ is given by

Answer:

Answer: D

We know that:

Δ = Sum of the product of the elements of a column (or a row) with their corresponding cofactors

∴Δ = a11A11 + a21A21 + a31A31

Hence, the value of Δ is given by the expression given in alternative D.

The correct answer is D.

Page No 131:

Question 1:

Find adjoint of each of the matrices.

Answer:

Question 2:

Find adjoint of each of the matrices.

Answer:

Question 3:

Verify A (adj A) = (adj A) A = I .

Answer:

Question 4:

Verify A (adj A) = (adj A) A = I .

Answer:

Page No 132:

Question 5:

Find the inverse of each of the matrices (if it exists).

Answer:

Question 6:

Find the inverse of each of the matrices (if it exists).

Answer:

Question 7:

Find the inverse of each of the matrices (if it exists).

Answer:

Question 8:

Find the inverse of each of the matrices (if it exists).

Answer:

Question 9:

Find the inverse of each of the matrices (if it exists).

Answer:

Question 10:

Find the inverse of each of the matrices (if it exists).

.

Answer:

Question 11:

Find the inverse of each of the matrices (if it exists).

Answer:

Question 12:

Let and. Verify that 

Answer:

From (1) and (2), we have:

(AB)−1 = B−1A−1

Hence, the given result is proved.

Question 13:

If, show that. Hence find.

Answer:

Question 14:

For the matrix, find the numbers a and b such that A2 + aA + bI = O.

Answer:

We have:

Comparing the corresponding elements of the two matrices, we have:

Hence, −4 and 1 are the required values of a and b respectively.

Question 15:

For the matrixshow that A3 − 6A2 + 5A + 11 I = O. Hence, find A−1.

Answer:

From equation (1), we have:

Question 16:

If verify that A3 − 6A2 + 9A − 4I = O and hence find A−1

Answer:

From equation (1), we have:

Question 17:

Let A be a nonsingular square matrix of order 3 × 3. Then  is equal to

A.  B.  C.  D. 

Answer:

Answer: B

We know that,

Hence, the correct answer is B.

Question 18:

If A is an invertible matrix of order 2, then det (A−1) is equal to

A. det (A) B.  C. 1 D. 0

Answer:

Since A is an invertible matrix, 

Hence, the correct answer is B.

Page No 136:

Question 1:

Examine the consistency of the system of equations.

x + 2y = 2

2x + 3y = 3

Answer:

The given system of equations is:

x + 2y = 2

2x + 3y = 3

The given system of equations can be written in the form of AX = B, where

∴ A is non-singular.

Therefore, A−1 exists.

Hence, the given system of equations is consistent.

Question 2:

Examine the consistency of the system of equations.

2x − y = 5

x + y = 4

Answer:

The given system of equations is:

2x − y = 5

x + y = 4

The given system of equations can be written in the form of AX = B, where

∴ A is non-singular.

Therefore, A−1 exists.

Hence, the given system of equations is consistent.

Question 3:

Examine the consistency of the system of equations.

x + 3y = 5

2x + 6y = 8

Answer:

The given system of equations is:

x + 3y = 5

2x + 6y = 8

The given system of equations can be written in the form of AX = B, where

∴ A is a singular matrix.

Thus, the solution of the given system of equations does not exist. Hence, the system of equations is inconsistent.

Question 4:

Examine the consistency of the system of equations.

x + y + z = 1

2x + 3y + 2z = 2

ax + ay + 2az = 4

Answer:

The given system of equations is:

x + y + z = 1

2x + 3y + 2z = 2

ax + ay + 2az = 4

This system of equations can be written in the form AX = B, where

∴ A is non-singular.

Therefore, A−1 exists.

Hence, the given system of equations is consistent.

Question 5:

Examine the consistency of the system of equations.

3x − y − 2z = 2

2y − z = −1

3x − 5y = 3

Answer:

The given system of equations is:

3x − y − 2z = 2

2y − z = −1

3x − 5y = 3

This system of equations can be written in the form of AX = B, where

∴ A is a singular matrix.

Thus, the solution of the given system of equations does not exist. Hence, the system of equations is inconsistent.

Question 6:

Examine the consistency of the system of equations.

5x − y + 4z = 5

2x + 3y + 5z = 2

5x − 2y + 6z = −1

Answer:

The given system of equations is:

5x − y + 4z = 5

2x + 3y + 5z = 2

5x − 2y + 6z = −1

This system of equations can be written in the form of AX = B, where

∴ A is non-singular.

Therefore, A−1 exists.

Hence, the given system of equations is consistent.

Question 7:

Solve system of linear equations, using matrix method.

Answer:

The given system of equations can be written in the form of AX = B, where

Thus, A is non-singular. Therefore, its inverse exists.

Question 8:

Solve system of linear equations, using matrix method.

Answer:

The given system of equations can be written in the form of AX = B, where

Thus, A is non-singular. Therefore, its inverse exists.

Question 9:

Solve system of linear equations, using matrix method.

Answer:

The given system of equations can be written in the form of AX = B, where

Thus, A is non-singular. Therefore, its inverse exists.

Question 10:

Solve system of linear equations, using matrix method.

5x + 2y = 3

3x + 2y = 5

Answer:

The given system of equations can be written in the form of AX = B, where

Thus, A is non-singular. Therefore, its inverse exists.

Question 11:

Solve system of linear equations, using matrix method.

Answer:

The given system of equations can be written in the form of AX = B, where

Thus, A is non-singular. Therefore, its inverse exists.

Question 12:

Solve system of linear equations, using matrix method.

x − y + z = 4

2x + y − 3z = 0

x + y + z = 2

Answer:

The given system of equations can be written in the form of AX = B, where

Thus, A is non-singular. Therefore, its inverse exists.

Question 13:

Solve system of linear equations, using matrix method.

2x + 3y + 3z = 5

x − 2y + z = −4

3x − y − 2z = 3

Answer:

The given system of equations can be written in the form AX = B, where

Thus, A is non-singular. Therefore, its inverse exists.

Question 14:

Solve system of linear equations, using matrix method.

x − y + 2z = 7

3x + 4y − 5z = −5

2x − y + 3z = 12

Answer:

The given system of equations can be written in the form of AX = B, where

Thus, A is non-singular. Therefore, its inverse exists.

Page No 137:

Question 15:

If, find A−1. Using A−1 solve the system of equations

Answer:

Now, the given system of equations can be written in the form of AX = B, where

Question 16:

The cost of 4 kg onion, 3 kg wheat and 2 kg rice is Rs 60. The cost of 2 kg onion, 4 kg

wheat and 6 kg rice is Rs 90. The cost of 6 kg onion 2 kg wheat and 3 kg rice is Rs 70.

Find cost of each item per kg by matrix method.

Answer:

Let the cost of onions, wheat, and rice per kg be Rs x, Rs y,and Rs z respectively.

Then, the given situation can be represented by a system of equations as:

This system of equations can be written in the form of AX = B, where

Now,

X = A−1 B

Hence, the cost of onions is Rs 5 per kg, the cost of wheat is Rs 8 per kg, and the cost of rice is Rs 8 per kg.

Page No 141:

Question 1:

Prove that the determinant is independent of θ.

Answer:

Hence, Δ is independent of Î¸.

Question 2:

Without expanding the determinant, prove that

Answer:

Hence, the given result is proved.

Question 3:

Evaluate 

Answer:

Expanding along C3, we have:

Question 4:

If a, b and c are real numbers, and,

Show that either a + b + c = 0 or a = b = c.

Answer:

Expanding along R1, we have:

Hence, if Δ = 0, then either a + b + c = 0 or a = b = c.

Question 5:

Solve the equations 

Answer:

Question 6:

Prove that 

Answer:

Expanding along R3, we have:

Hence, the given result is proved.

Question 7:

If 

Answer:

We know that.

Page No 142:

Question 8:

Let verify that

(i) 

(ii) 

Answer:

(i)

We have,

(ii)

Question 9:

Evaluate 

Answer:

Expanding along R1, we have:

Question 10:

Evaluate 

Answer:

Expanding along C1, we have:

Question 11:

Using properties of determinants, prove that:

Answer:

Expanding along R3, we have:

Hence, the given result is proved.

Question 12:

Using properties of determinants, prove that:

Answer:

Expanding along R3, we have:

Hence, the given result is proved.

Question 13:

Using properties of determinants, prove that:

Answer:

Expanding along C1, we have:

Hence, the given result is proved.

Question 14:

Using properties of determinants, prove that:

Answer:

Expanding along C1, we have:

Hence, the given result is proved.

Question 15:

Using properties of determinants, prove that:

Answer:

Hence, the given result is proved.

Question 16:

Solve the system of the following equations

Answer:

Let 

Then the given system of equations is as follows:

This system can be written in the form of AX = B, where

A

Thus, A is non-singular. Therefore, its inverse exists.

Now,

A11 = 75, A12 = 110, A13 = 72

A21 = 150, A22 = −100, A23 = 0

A31 = 75, A32 = 30, A33 = − 24

Page No 143:

Question 17:

Choose the correct answer.

If a, b, c, are in A.P., then the determinant

A. 0 B. 1 C. x D. 2x

Answer:

Answer: A

Here, all the elements of the first row (R1) are zero.

Hence, we have Δ = 0.

The correct answer is A.

Question 18:

Choose the correct answer.

If x, y, z are nonzero real numbers, then the inverse of matrix is

A.  B. 

C.  D. 

Answer:

Answer: A

The correct answer is A.

Question 19:

Choose the correct answer.

Let, where 0 ≤ θ≤ 2π, then

A. Det (A) = 0

B. Det (A) ∈ (2, ∞)

C. Det (A) ∈ (2, 4)

D. Det (A)∈ [2, 4]

Answer:

Answer: D

 Now,

0≤θ≤2π

⇒-1≤sinθ≤1 The correct answer is D.

NCERT Solutions for Class 12 Maths

  • Chapter 1 – Relations and Functions
  • Chapter 2 – Inverse Trigonometric Functions
  • Chapter 3 – Matrices
  • Chapter 4 – Determinants
  • Chapter 5 – Continuity and Differentiability
  • Chapter 6 – Application of Derivatives
  • Chapter 7 – Integrals
  • Chapter 8 – Applications of Integrals
  • Chapter 9 – Differential Equations
  • Chapter 10 – Vector Algebra
  • Chapter 11 – Three dimensional Geometry
  • Chapter 12 – Linear Programming
  • Chapter 13 – Probability
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