# Superposition of cosine functions for tides

1. Aug 21, 2008

### flyinghigh

1. The problem statement, all variables and given/known data
I have 1.805cos(2pi / 12.165x) +3.125 as the function of tidal data. However I need to use another function, superimpose, to more accurately graph the data for the tides. And yeah I'm pretty lost... Does the next function have to be something to do wit the moon and its rotation around earth?

And help would be greatly appreciated :)

2. Aug 21, 2008

### HallsofIvy

Staff Emeritus
I have no idea what you are asking! Why is that not accurate? What do you mean by "superimpose" another function?

3. Aug 21, 2008

### flyinghigh

Sorry, should of explained that to find a more accurate representation of the tide, you use the sum of two cosine functions, which is also known as superposition. So yeah, the tide is represented by y1+y2, where y1=the above function, y2=??...

4. Aug 21, 2008

### HallsofIvy

Staff Emeritus
that obviously depends upon the data!

5. Aug 21, 2008

### flyinghigh

Well then what area of the data? Since I already have the first function that takes into account the tide heights and occurence, what else is required? That's why I asked if it was based on the moon's orbit etc.

6. Aug 22, 2008

### flyinghigh

7. Aug 22, 2008

### Defennder

You have to be more explicit. What does that mean? What is x? What are you trying to show?

8. Aug 22, 2008

### flyinghigh

1.805 is the amplitude of the waves, as in the average difference between the high tide and the low tide. 2pi/12.165x is the period of the tide, as in how frequently it occurs. 3.125 is the average water height and hence the vertical phase shift of the function. So then I need another function in the same form, as in y=Acos(Bx-C)+D, that I then add to my function.

I'm trying to show, more accurately, tidal data. I think the second function has to be something to do with the moon and it's effects on certain tides? But yeah anyone who know's what they're talking about please help!

Thanks

flyinghigh