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Let A=[222022002]A=\begin{bmatrix}2 & 2 & 2 \\ 0 & 2 & 2 \\ 0 & 0 & 2\end{bmatrix}, then A6A^6 is equal to:

Solution

✅ Correct Option: 2

Write A=2(I+U)A = 2(I+U) where UU has 11s above the diagonal.

Since U3=0U^3 = 0, (I+U)6=I+6U+15U2(I+U)^6 = I+6U+15U^2.

This gives [1621016001]\begin{bmatrix}1&6&21\\0&1&6\\0&0&1\end{bmatrix} (the 2121 comes from 6+156+15), so A6=26A^6 = 2^6 times that matrix.

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