There exist an infinite number of functions that will give those (finite number of) points. What you have, A cos((pi/12)t+ 240)+ D, won't work. That would have each loop going up to A+ D and Down to D- A, not varying as in your graph.
A cos((pi/12)t+ 240)+ D is not correct?
I know that it wouldn't work because I need to find A and D. But I think cos((pi/12)t+ 240) is correct at least.
[Acos(Bt+C)+D] ----> B and C are constant in this graphic I think.
What kind of trigonometric function describes this graph?