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**sinewave85** Ok, I am studying for a test and working through some practice problems on a handout from teacher. The problem is, I am getting a different answer than the one he gives for this application problem:

"A tractor tire has a diameter of 6 feet and is revolving at a rate of 45 rpm. At t=0 a certain point is at height 0.

A) Write an equation with phase shift 0 to describe the height of the point above the ground after 't' seconds.

B) How high is the point above the ground after 28 seconds?"

I get this:

h = -3cos(t*8pi/3) + 3

and at t = 28, h = 4.5

but the answer given is this:

h = -3cos(t*3pi/2)+3

and at t = 28, h = 0

The difference is the value for k, which I got by converting the period from revs per min (45/1) to rev per second (45/60 or 3/4), and then k = 2pi(4/3). The supplied answer inverts this, and I am wondering if this is a mistake or if I am looking at it incorrectly. Thanks.