Observe that& nbsp;
\[ A^{2026}-A^{2025} = A^{2025}(A-I). \]
Taking determinants,
\[ \left|A^{2026}-A^{2025}\right| = |A^{2025}|\;|A-I|. \]
Now,
\[ A-I= \begin{bmatrix} 2025 & amp; 2025 & amp; 2024\\ 2025 & amp; 2023 & amp; 2023\\ 2024 & amp; 2023 & amp; 2021 \end{bmatrix}. \]
Since
\[ R_1-2R_2+R_3=0, \]
the rows are linearly dependent.
Hence,
\[ |A-I|=0. \]
Therefore,
\[ \boxed{\left|A^{2026}-A^{2025}\right|=0.} \]
Thus, the correct option is
\[ \boxed{(D)}. \]
Consider the linear system of equations \[ \begin{bmatrix} 3 & -1 & 4 \\ 6 & 3 & 1 \end{bmatrix} \begin{bmatrix} x \\ y \\ z \end{bmatrix} = \begin{bmatrix} 1 \\ 1 \end{bmatrix}. \] In this system of equations, if \(x\) is always a fixed constant, then the system has:& nbsp;