I am unable to solve this problem from matrix computation book by Gene H. Golub.
Show that if $A$ and $B^H$ are in $\mathbb{C}^{m\times n}$ with $m\geq n$, then $\lambda(AB)$ = $\lambda(BA) \cup$ $\underbrace{\{0,...,0\}}_\text{m-n}$
Kindly help me solve this problem