If \( A = \begin{pmatrix} 1 & 0 \\ 1 & 1 \end{pmatrix} \), then \( A^n + nI \) is equal to:
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For matrices of the form \( \begin{pmatrix} 1 & 0 k & 1 \end{pmatrix} \), the \( n \)-th power is simply \( \begin{pmatrix} 1 & 0 nk & 1 \end{pmatrix} \). This is a very common shortcut in entrance exams.