Understanding the Equation for Waves on a String: Help Needed!

[ajmCane22]

Homework Statement

A wave on a string is described by the following equation: y = (15cm)cos(πx/5.0cm - πt/12s). Sketch this wave from x = 0 to x = 10 cm for the t = 0.

The Attempt at a Solution

Honestly, I've never seen this notation before. I have no idea how to interpret it. I tried googling some help and now I'm more confused. I tried setting t to 0 and putting different values for x in order to get a value for y, but I get 14.9... for every value of x, which gives me a straight line, and that answer was incorrect. It might be hard to explain this online, but I would appreciate it immensely if somebody would please try. I'm utterly lost.

 

[ojs]

Then you are doing something wrong in your calculations or choosing to few x's.
For instance, if x = 0 then y = 15, if x = 2,5 then y = 0, if x = 5 then y = -15 and so on.
How are you doing the calculations?

 

[ajmCane22]

This is what I am doing:

Using x=2.5 for example,

t=0, so...
15 x cos[(pi*2.5)/5.0 - (pi*0)/12]
15 x cos(1.57 - 0)
15 x 0.9996 = 14.99

I'm obviously doing something wrong, because I know for x=2.5 y should equal 0

 

[ojs]

your calculator is set to degrees, it should be set to radians.

 

[ajmCane22]

Omg...I feel like a complete moron.