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If A and B are square matrices of order 3 such that |A| = -1 and |B| = 5, then the value of |3AB| is

Solution

✅ Correct Option: 4

Given:

  • A and B are square matrices of order 3
  • ∣A∣=−1|A| = -1
  • ∣B∣=5|B| = 5

For an n×nn \times n matrix M and scalar k:

∣kM∣=kn×∣M∣|kM| = k^n \times |M|

For matrices A and B:

∣AB∣=∣A∣×∣B∣|AB| = |A| \times |B|


Since the matrices are of order 3:

∣3AB∣=33×∣AB∣|3AB| = 3^3 \times |AB|

∣3AB∣=27×∣AB∣|3AB| = 27 \times |AB|


Finding ∣AB∣|AB|:

∣AB∣=∣A∣×∣B∣|AB| = |A| \times |B|

∣AB∣=(−1)×5|AB| = (-1) \times 5

∣AB∣=−5|AB| = -5


∣3AB∣=27×∣AB∣|3AB| = 27 \times |AB|

∣3AB∣=27×(−5)|3AB| = 27 \times (-5)

∣3AB∣=−135|3AB| = -135

Therefore, the value of ∣3AB∣=−135|3AB| = -135

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