Target Exam

CUET

Subject

-- Applied Mathematics - Section B2

Chapter

Algebra

Question:

If $A =\begin{bmatrix}5&6\\3&2\end{bmatrix}$ then which of the following is correct?

(A) $|A|$ is positive
(B) $|adj\, A| = -8$
(C) Cofactor of 3 is 6
(D) $|2A| = -32$

Choose the correct answer from the options given below:

Options:

(B) and (D) only

(A), (B) and (C) only

(A), (C) and (D)

(C) and (D) only

Correct Answer:

(B) and (D) only

Explanation:

The correct answer is Option (1) → (B) and (D) only **

$A=\begin{bmatrix}5 & 6 \\ 3 & 2\end{bmatrix}$

Determinant:

$|A| = 5\cdot2 - 6\cdot3 = 10 - 18 = -8$

(A) $|A|$ is positive → false (it is $-8$)

(B) $|\text{adj}\,A| = -8$

For a $2\times2$ matrix: $|\text{adj}\,A| = |A|^{1} = -8$ → true

(C) Cofactor of $3$:

Cofactor of $3 = (-1)^{2+1}\cdot\text{minor} = -\left|\begin{matrix}6\end{matrix}\right| = -6$ → not $6$ → false

(D) $|2A|$:

$|2A| = 2^{2}|A| = 4(-8) = -32$ → true

Correct statements: (B) and (D)