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Determinants, Adjoint & Inverse · Question 68 of 87

Question 68

HardOriginal question

AA is a square matrix of order 3 with ∣A∣=2|A| = 2. What is ∣3A−1∣|3A^{-1}|?

Options for question 68

Show the answer and explanation
CorrectNot quiteAnswer D

Correct answer: D

Explanation

  1. ∣kB∣=kn∣B∣|kB| = k^{n}|B| for order nn, and ∣A−1∣=1∣A∣|A^{-1}| = \frac{1}{|A|}.

  2. ∣3A−1∣=33×12=272|3A^{-1}| = 3^{3} \times \frac{1}{2} = \frac{27}{2}.

Worth noting

32\frac{3}{2} multiplies by 3 once; a scalar comes out of each of the 3 rows.

Concept
Determinant of a multiple of the inverse
Typical time
120 s
Your time
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The rule this testsThe adjoint and the inverse
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Ten questions from Determinants, Adjoint & Inverse, at your own pace.

Practise this chapter →

Ten questions from Determinants, Adjoint & Inverse, at your own pace.