Question

The position of some object moving along the x-axis is observed to be x(t)=9cos(pi*t/3+pi/4) meters. Find the frequency.

Answer 1

(pi t/3) is all that matters. I assume t in seconds.
at t = 0 that is 0
when is it 2 pi?
pi T/3 = 2 pi
T = 6 seconds period
f = 1/T = 1/6 Hz