Calculus
posted by Tim on .
A ship sailing parallel to shore sights a lighthouse at an angle of 12 degrees from its direction of travel. After traveling 5 miles farther, the angle is 22 degrees. At that time, how far is the ship from the lighthouse?

Let the lighthouse be h miles from shore. Let x be the distance of the ship from a point on shore closest to the lighthouse.
h/(x+5) = tan 12°
h/x = tan 22°
so, equating h,
(x+5)tan 12° = x tan 22°
.212(x+5) = .404x
1.06 = .282x
x = 3.759 mi
Now, the distance of the ship from the lighthouse, d, can be found by
3.759/d = cos 22°
d = 4.05 mi