Prove that if $A$ is an $m \times n$ matrix and $B$ is an $n \times m$ matrix, then $\text{trace}(AB) = \text{trace}(BA)$.

Question

Not sure how to start this proof, it's for linear algebra.

Prove that if $A$ is an $m \times n$ matrix and $B$ is an $n \times m$ matrix, then $\text{trace}(AB) = \text{trace}(BA)$.