3. ) During the autumnal equinox, the surface temperature (°C) of the water of a lake x hours after sunrise was recorded over a 24 hour period. The results are shown in the graph below. If y represents the surface temperature of the water x hours after sunrise, the variation in temperature can be approximated by a cosine function of the form y= A cos Bx+ D. Find the equation. Explain your reasoning and show your work. Temperature (°C) 20 20 y 15 10 50 12 18 T 24 Number of Hours after Sunrise