Let a,b∈Ra, b \in \mathbb{R}a,b∈R with b≠0b \ne 0b=0. Consider the matrix A=(a−bba)A = \begin{pmatrix} a & -b \\ b & a \end{pmatrix}A=(ab−ba). What are the eigenvalues of AAA?
a±iba \pm iba±ib
a±ba \pm ba±b
b±iab \pm iab±ia
±a2+b2\pm \sqrt{a^2 + b^2}±a2+b2