Class 12 Maths MCQ – Determinants

1. What is the determinant of a 2×2 matrix [[a,b],[c,d]]?

a) ad+bc
b) ad-bc
c) ab+cd
d) a+b+c+d

Answer:

b) ad-bc

Explanation:

Determinant of [[a,b],[c,d]] is ad-bc.

2. The determinant of an identity matrix of any order is:

a) 0
b) 1
c) -1
d) 2

Answer:

b) 1

Explanation:

Determinant of the identity matrix is always 1.

3. If two rows (or columns) of a determinant are identical, then its value is:

a) 0
b) 1
c) -1
d) Undefined

Answer:

a) 0

Explanation:

If two rows or columns are identical, the determinant value is 0.

4. What is the result of interchanging two rows (or columns) of a determinant?

a) Determinant is halved
b) Determinant remains unchanged
c) Determinant becomes negative of the original
d) Determinant becomes zero

Answer:

c) Determinant becomes negative of the original

Explanation:

Interchanging two rows or columns changes the sign of the determinant.

5. The determinant of a singular matrix is:

a) 1
b) 0
c) -1
d) Undefined

Answer:

b) 0

Explanation:

A matrix is singular if its determinant is zero.

6. If each element of a row (or column) of a determinant is multiplied by 'k', the determinant:

a) Remains unchanged
b) Becomes k times the original
c) Becomes 1/k times the original
d) Becomes k^2 times the original

Answer:

b) Becomes k times the original

Explanation:

The determinant value gets multiplied by the factor 'k'.

7. If A is a matrix of order 3×3, the determinant of 2A is:

a) 8 times det(A)
b) 2 times det(A)
c) 6 times det(A)
d) 4 times det(A)

Answer:

a) 8 times det(A)

Explanation:

The determinant gets multiplied by 2^3 = 8.

8. If det(A) = 5, then the determinant of its inverse, det(A^(-1)), is:

a) 1/5
b) 5
c) -5
d) 0

Answer:

a) 1/5

Explanation:

det(A^(-1)) is the reciprocal of det(A).

9. For any matrix A, det(At) is:

a) det(A)
b) -det(A)
c) 1/det(A)
d) 0

Answer:

a) det(A)

Explanation:

The determinant of the transpose of A is the same as the determinant of A.

10. If two matrices A and B are of the same order, then det(A+B) is:

a) det(A) + det(B)
b) det(A) – det(B)
c) Not necessarily equal to det(A) + det(B)
d) Always 0

Answer:

c) Not necessarily equal to det(A) + det(B)

Explanation:

The determinant of the sum is not generally the sum of the determinants.

11. A determinant remains unchanged if:

a) Rows are converted to columns
b) All elements are squared
c) Rows are multiplied by a scalar
d) None of the above

Answer:

a) Rows are converted to columns

Explanation:

This means taking the transpose, which doesn’t change the determinant value.

12. For any 2×2 matrix [[a,b],[c,d]], if det(A) = 0, then:

a) a = d
b) a = -d
c) bc = ad
d) ad = bc

Answer:

d) ad = bc

Explanation:

Because ad-bc = 0.

13. If A and B are both 3×3 matrices, then det(AB) is:

a) det(A) + det(B)
b) det(A) det(B)
c) det(A) – det(B)
d) det(A/B)

Answer:

b) det(A) det(B)

Explanation:

The determinant of the product is the product of the determinants.

14. The determinant value of the matrix [[2,4],[1,2]] is:

a) 0
b) 4
c) 2
d) 1

Answer:

a) 0

Explanation:

Using the formula, 2*2 – 4*1 = 0.

15. If a determinant has a row of zeros, its value is:

a) 1
b) -1
c) 0
d) Undefined

Answer:

c) 0

Explanation:

Any determinant with a full row or column of zeros has a value of 0.

16. If B is obtained from A by adding a row of A multiplied by k to another row, then det(B) is:

a) det(A) + k
b) k det(A)
c) det(A)
d) 0

Answer:

c) det(A)

Explanation:

Elementary row operations of this type don't change the determinant.

17. For a triangular matrix (either lower or upper triangular), the determinant is:

a) 0
b) Product of diagonal elements
c) 1
d) Undefined

Answer:

b) Product of diagonal elements

Explanation:

For a triangular matrix, the determinant is the product of its diagonal elements.

18. The value of the determinant [[0,1,2],[3,4,5],[6,7,8]] is:

a) 0
b) 3
c) 1
d) -3

Answer:

a) 0

Explanation:

This determinant has two identical rows when expanded, making its value 0.

19. If A is a 3×3 matrix and k is a scalar, then det(kA) is:

a) k det(A)
b) k^3 det(A)
c) k^2 det(A)
d) det(A)/k

Answer:

b) k^3 det(A)

Explanation:

For a 3×3 matrix, the factor k is raised to the power of the order.

20. The determinant value of the 2×2 zero matrix is:

a) 1
b) 0
c) -1
d) Undefined

Answer:

b) 0

Explanation:

The determinant of the zero matrix is always 0.

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