Solution
= Solution
By the given <matrix similarity>, $A'=P^{-1}AP$ for an invertible $P$. Hence
$$
\det(tI-A')=\det\{P^{-1}(tI-A)P\}
=\det(P^{-1})\det(tI-A)\det(P)=\det(tI-A).
$$
The <characteristic polynomials> are identical. Therefore \b[the characteristic equations and <eigenvalues>, including algebraic multiplicities, agree]. The conclusion is independent of the choice between $\det(tI-A)$ and $\det(A-tI)$ conventions.