Problem

The average daytime temperature for a city is given by the function

D(t) = 5 \cos\left(\frac{\pi}{6}t\right) + 20

°C, where

t

is the time in months after January. a. Sketch the graph of

D

against

t

for

0 \le t \le 24

. b. Find the average daytime temperature during May. c. Find the minimum average daytime temperature, and the month in which it occurs.