Two coherent waves, coming from sources at different locations, move along the $x$ axis. Their wave functions are
$$
E_{1}=(860 \mathrm{V} / \mathrm{m}) \sin \left[\frac{2 \pi x_{1}}{650 \mathrm{nm}}-2 \pi(462 \mathrm{THz}) t+\frac{\pi}{6}\right]
$$
and
$$
E_{2}=(860 \mathrm{V} / \mathrm{m}) \sin \left[\frac{2 \pi x_{2}}{650 \mathrm{nm}}-2 \pi(462 \mathrm{THz}) t+\frac{\pi}{8}\right]
$$
Determine the relationship between $x_{1}$ and $x_{2}$ that produces constructive interference when the two waves are superposed.