# Plane Trigonometry

**Problem**

The tide in Bay of Fundy rises and falls every 13 hours. The depth of the water at a certain point in the bay is modeled by a function *d* = 5 sin (2π/13)*t* + 9, where *t* is time in hours and *d* is depth in meters. Find the depth at *t* = 13/4 (high tide) and *t* = 39/4 (low tide).

- The depth of the high tide is 15 meters and the depth of the low tide is 3 meters.
- The depth of the high tide is 16 meters and the depth of the low tide is 2 meters.
- The depth of the high tide is 14 meters and the depth of the low tide is 4 meters.
- The depth of the high tide is 17 meters and the depth of the low tide is 1 meter.

**Problem**

The number of hours daylight, *D*(*t*) at a particular time of the year can be approximated by

$D(t) = \dfrac{K}{2}\sin \left[ \dfrac{2\pi}{365}(t - 79) \right] + 12$

for *t* days and *t* = 0 corresponding to January 1. The constant *K* determines the total variation in day length and depends on the latitude of the locale. When is the day length the longest, assuming that it is NOT a leap year?

A. December 20 | C. June 20 |

B. June 19 | D. December 19 |