Given that $ A^{-1} = \frac{1}{7} \begin{bmatrix} 2 & 1 \\ -3 & 2 \end{bmatrix} $, matrix $ A $ is:
If \( A \) and \( B \) are two non-zero square matrices of the same order such that: $$ (A + B)^2 = A^2 + B^2, $$ then: