Let $A$ be the matrix $A = \begin{pmatrix} 1 & \sqrt{2}\\ -\sqrt{2} & -1\\ \end{pmatrix}$
Compute the matrix $B = 3A -2A^2 - A^3 -5A^4 + A^6$.
Could any one give me any hint for this one? I have calculated the eigenvalues they are $(1+\sqrt{2}i),(1-\sqrt{2}i)$