Class CBSE Class 12 Mathematics Matrices and Determinants Q #741
KNOWLEDGE BASED
APPLY
1 Marks 2024 MCQ SINGLE
If \(\begin{vmatrix}-a&b&c\\ a&-b&c\\ a&b&-c\end{vmatrix}= kabc,\) then the value of k is:
(A) 0
(B) 1
(C) 2
(D) 4

AI Tutor Explanation

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Step-by-Step Solution

Let's evaluate the determinant:

\[\begin{vmatrix}-a&b&c\\ a&-b&c\\ a&b&-c\end{vmatrix}\]

Apply \(R_1 \rightarrow R_1 + R_2\):

\[\begin{vmatrix}0&0&2c\\ a&-b&c\\ a&b&-c\end{vmatrix}\]

Expand along the first row:

\[0 \cdot C_{11} + 0 \cdot C_{12} + 2c \cdot C_{13} = 2c \begin{vmatrix}a&b\\ a&b\end{vmatrix}\]

Oops! There was an error in the row operation. Let's try a different approach.

Original determinant:

\[\begin{vmatrix}-a&b&c\\ a&-b&c\\ a&b&-c\end{vmatrix}\]

Apply \(C_1 \rightarrow C_1 + C_2\):

\[\begin{vmatrix}-a+b&b&c\\ a-b&-b&c\\ a+b&b&-c\end{vmatrix}\]

This doesn't seem to simplify things much either.

Let's try adding all rows to the first row: \(R_1 \rightarrow R_1 + R_2 + R_3\)

\[\begin{vmatrix}a&b&c\\ a&-b&c\\ a&b&-c\end{vmatrix}\]

Applying \(R_1 \rightarrow R_1 + R_2 + R_3\):

\[\begin{vmatrix}a+a+a&b-b+b&c+c-c\\ a&-b&c\\ a&b&-c\end{vmatrix} = \begin{vmatrix}a&b&c\\ a&-b&c\\ a&b&-c\end{vmatrix}\]

This is not correct either.

Let's evaluate the determinant directly:

\(\begin{vmatrix}-a&b&c\\ a&-b&c\\ a&b&-c\end{vmatrix} = -a((-b)(-c) - (c)(b)) - b((a)(-c) - (c)(a)) + c((a)(b) - (-b)(a))\)

\(= -a(bc - bc) - b(-ac - ac) + c(ab + ab)\)

\(= -a(0) - b(-2ac) + c(2ab)\)

\(= 0 + 2abc + 2abc\)

\(= 4abc\)

Therefore, \(kabc = 4abc\), which means \(k = 4\).

Correct Answer: 4

AI Suggestion: Option D

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student needs to apply the properties of determinants to simplify and solve for the unknown variable 'k'.
Knowledge Dimension: PROCEDURAL
Justification: The question requires the student to follow a specific procedure to evaluate the determinant and find the value of k. This involves applying properties of determinants and algebraic manipulation.
Syllabus Audit: In the context of CBSE Class 12, this is classified as KNOWLEDGE. The question directly tests the student's knowledge of determinants and their properties, which is a core topic in the syllabus.