Show that the hamiltonian operator for the one-electron atom
$$-\frac{\hbar^{2}}{2 m} \nabla^{2}-\frac{Z e^{2}}{4 \pi \epsilon_{0}}$$
commutes with the operator for the $z$ component of the angular momentum; i.e., show that $\hat{H}\left(\hat{A}_{l}\right)_{x}-\left(\hat{A}_{t}\right), \hat{H}=0$.