On September 6^th, 2017, there was a full moon. If t is the number of days since September 6^th, the percent of moon illuminated can be represented by

(a) Find H'(t). Explain what this tells about the moon.
(b) For 0 ≤ t ≤ 30, when is H'(t) = 0? What does this tell us about the moon?
(c) For 0 ≤ t ≤ 30, when is H'(t) negative? When is it positive? Explain what positive and negative values of H'(t) tell us about the moon.

H(t) = 50+ 50 cos (). 15