### Instruction: Find the phase shift of the graph of $y = \sin (3x - \pi).$.### Response: The phase shift of a sinusoidal function is the horizontal displacement of the graph from the standard function $y = \sin x.$
I can rewrite the given function as $y = \sin (3x - \pi) = \sin (3(x - \frac{\pi}{3})).$
This shows that the graph of the given function is obtained by taking the graph of $y = \sin (3x)$ and shifting it to the right by $\frac{\pi}{3}$ units.
Therefore, the phase shift of the graph of $y = \sin (3x - \pi)$ is $\frac{\pi}{3}$.