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If A is a square matrix of order 3×33 \times 3 and ∣A∣=4|A| = 4. The value of ∣(adjA).A∣|(adjA).A| is

Solution

✅ Correct Option: 3

Given that AA is a square matrix of order 3×33 \times 3 and ∣A∣=4|A| = 4.

For any square matrix AA:

(adjA)⋅A=∣A∣⋅I(adj A) \cdot A = |A| \cdot I

where II is the identity matrix.


Substituting ∣A∣=4|A| = 4:

(adjA)⋅A=4I(adj A) \cdot A = 4I

where II is the 3×33 \times 3 identity matrix.


Taking determinant on both sides:

∣(adjA)⋅A∣=∣4I∣|(adj A) \cdot A| = |4I|

For an n×nn \times n identity matrix multiplied by a constant kk:

∣kI∣=kn|kI| = k^n

Since the matrix is 3×33 \times 3:

∣4I∣=43|4I| = 4^3

∣4I∣=64|4I| = 64


Therefore, ∣(adjA)⋅A∣=64|(adj A) \cdot A| = 64

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