Answer
(a) $\frac{\pi}{2}$ and $\frac{\pi}{3}$
(b) $\frac{\pi}{6}$
(c) The curves are out of phase.
(d) see graph.
Work Step by Step
(a) Based on the definition that $b$ would be the phase in $y=Asin(kt-b)$,
the phase in $y_1$ is $\frac{\pi}{2}$, and the phase in $y_2$ is $\frac{\pi}{3}$
(b) The phase difference can be find as $\frac{\pi}{2}-\frac{\pi}{3}=\frac{\pi}{6}$
(c) Since the phase difference obtained in (b) is not multiples of $2\pi$, the curves are out of phase.
(d) The two curves are graphed on the same set of axies as shown in the figure.
