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If $A$ is a $2\times 2$ matrix and $P$ is an invertible matrix such that:

$$PAP^{-1}=\begin{pmatrix}2 &1 \\\ 0 & 2\end{pmatrix}$$

...then the characteristic polynomial for $A$ is:

$x^2-4$

$2-x$

$x^2-4x+4$

Impossible to determine without more information