The identity matrix $I_{n}$ is a square matrix with ones on the main diagonal and zeros elsewhere. For a 2x2 matrix, $I_{n}$ is:
$$I_{n} = \left[\begin{array}{ll}
1 & 0 \\
0 & 1
\end{array}\right]$$
So, $A-\lambda I_{n}$ is:
$$A-\lambda I_{n} =
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