(Sorry, posting a lot of threads tonight. Exams coming up, past papers are surprisingly unlike my notes )

A = $\displaystyle \begin{pmatrix}0&1\\1&0\end{pmatrix}$

Determine all 2 x 2 matrices B such that AB-BA = $\displaystyle \begin{pmatrix}1&0\\0&-1\end{pmatrix}$

I really don't know how to even start this one. Could anybody give any pointers?