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Let A=[x101]A = \begin{bmatrix} x & 1 \\ 0 & 1 \end{bmatrix} where xx is a real number, and B=[223+201]B = \begin{bmatrix} 2\sqrt{2} & 3 + \sqrt{2} \\ 0 & 1 \end{bmatrix}. If A3=BA^3 = B, then xx is equal to

Solution

✅ Correct Option: 2

Since A3=BA^3 = B, their determinants must also be equal.

Also, We know that ∣A3∣=∣A∣3|A^3| = |A|^3.

Now, finding the determinant of AA:

∣A∣=∣x101∣|A| = \begin{vmatrix} x & 1 \\ 0 & 1 \end{vmatrix} =x(1)−0(1)=x= x(1) - 0(1) = x

Therefore, ∣A3∣=∣A∣3=x3|A^3| = |A|^3 = x^3

Next, finding the determinant of BB:

∣B∣=∣223+201∣|B| = \begin{vmatrix} 2\sqrt{2} & 3+\sqrt{2} \\ 0 & 1 \end{vmatrix}

=22(1)−0(3+2)=22= 2\sqrt{2}(1) - 0(3+\sqrt{2}) = 2\sqrt{2}

Since ∣A3∣=∣B∣|A^3| = |B|,

x3=22=(2)3x^3 = 2\sqrt{2} = (\sqrt{2})^3

Hence, x=2x = \sqrt{2}.

The answer is Option 2: 2\sqrt{2}

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