$A= \begin{pmatrix} 1 & 2+3i \\ 2-3i & -1 \end{pmatrix}$
What is matrix $B$ such that $B^2=A$?
Its eigenvalues are $\sqrt{14}, -\sqrt{14}$
and I tried to use formula $B=U\sqrt{\lambda}U^{H}$ where $U$ is unitary matrix.
But then $\sqrt{ }$ of $-\sqrt{14}$ is not possible.
How can I solve this?