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If A=[1ab2]A = \begin{bmatrix} 1 & a \\ b & 2 \end{bmatrix} and B=[a12−3b]B = \begin{bmatrix} a & 1 \\ 2 & -3b \end{bmatrix} such that ∣AB∣=∣2B∣\lvert AB\rvert = \lvert 2B\rvert and ab≠−23ab \neq -\dfrac{2}{3} then:

A. ∣A∣=2\lvert A\rvert = 2

B. ∣A∣=4\lvert A\rvert = 4

C. ∣B∣=2\lvert B\rvert = 2

D. ∣B∣=4\lvert B\rvert = 4

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 2

∣AB∣=∣A∣∣B∣|AB|=|A||B| and ∣2B∣=4∣B∣|2B|=4|B| for order 2.

Since ∣B∣=−3ab−2≠0|B|=-3ab-2\neq 0 (given ab≠−23ab\neq -\frac23), we cancel to get ∣A∣=4|A|=4.

Then 2−ab=42-ab=4 gives ab=−2ab=-2, so ∣B∣=6−2=4|B|=6-2=4.

Hence B and D are true.

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