An object undergoing simple harmonic motion with a period T is at the position x = 0 at the time t = 0. At the time t = 0.25T the position of the object is positive. State whether x is positive, negative, or zero at the following times:
(a) t = 1.5T,
(b) t = 2T,
(c) t = 2.25T,
(d) t = 6.75T.