How to get the equation from a graph

Hi.

I'm trying to get an equation from a set of points and a graph but I can't figure it out.

So far I have: Acos((pi/12)t+240)+D I hope it's correct :)

http://img203.imageshack.us/img203/2530/dataok.jpg

I just need to find out A (amplitude) and D. A and D variate with time but I don't know how to get it. Never done any problem like this before.

Re: How to get the equation from a graph

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.

Re: How to get the equation from a 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?