Answer:
[tex]y=0.35cos(\frac{2\pi }{5.4 days}x)+4.0[/tex]
Explanation:
Since we have peak brightness at t=0 we should use a cosine formula to model this oscillatory phenomena, which will be [tex]y=Acos(kx)+B[/tex]. The average of this formula is B, since the cosine part cancels out when averaging, so B=4.0. The brightness variation is the amplitude of the formula, A=0.35, and since [tex]k=\frac{2\pi }{T}[/tex] we finally have [tex]y=0.35cos(\frac{2\pi }{5.4 days}x)+4.0[/tex]
