Answer
(a) $T/2$ seconds (b) $3T/4$ seconds
Work Step by Step
The period is the time it takes for the particle to go from the amplitude, to the negative amplitude, back to the positive amplitude. This distance is $2A+2A=4A$. Therefore, to travel half that distance, $2A$, it must take $T/2$ s. To travel $3A$, it must take three-fourths the total period time, $3T/4$.
