Graphing and finding trig function with given data

Another trig question i'm not getting right is the following:

"A population of animals oscillates sinusoidally between a low of 300 on January 1 and a high of 1200 on July 1. Graph the population against time and use your graph to find a formula for the population *P* as a function of time *t*, in months since the start of the year. Assume that the period of *P* is one year."

From that, I plugged in the following variables to the formula f(t) = Asin(B(t+h))+C

A = ((1200-300)/2) = 450

period = 12m --> 2π/B = 12, B = π/6

h (right horizontal shift) = -3

c (upwards vertical shift) = 750

and I got

f(t) = 450sin( π/6(t-3)+750

which looks fine on my calculator, but is wrong according to my h/w. I can't seem to find where I messed up, or of I am missing something entirely.

Any help is greatly appreciated.

Re: Graphing and finding trig function with given data

Hey rodryk.

In your problem, does January first correspond to x = 0? If so your value should be -3*pi/2 radians.