The Trace of $\mathbf{A}\mathbf{B}$ is the Trace of $\mathbf{B}\mathbf{A}$ and the generalization is that we can cycle matrices in a product an leave the Trace unchanged. An enjoyable bonus is to easily show that the a diagonalizable matrix's Trace is equal to the sum of its eigenvalues (this is true for all square matrices).
Best consumed by 2016/11/14
