The desert temperature,H, oscillates daily between 39ºF at 6am and 79ºF at 6pm. Write a possible formula forHin terms oft, measured in hours from 6am. Use the form:

H=Acos(Bt) +C.

What I tried was this: I subtracted 39 from 79 to get 40, then divided that in half. That should be the amplitude A, right? Then I took 12 hours (from 6am to 6pm), and set that equal to 2pi / b, the period for a cosine function. I got pi/6, which should be B. Then to get the y axis up to 40, C should be 20 since the amplitude is 20.

However, when I submitted this, all of them were wrong. Having tried everything I can think of, I'm asking for help. I'd appreciate any responses! Thank you!