🔍 Key Concepts

• Mid-latitude sailing formulas for course and distance • How to find difference of latitude (DLat) and difference of longitude (DLon), including E/W sign • Using cosine of mid-latitude to convert DLon (in minutes) to departure

💭 Think About

• First, compute DLat between the two positions, being careful with N/S, and convert it to minutes of arc. Is it getting more southerly or more northerly? • Next, compute DLon in minutes of arc and decide if it is easterly or westerly. Then adjust DLon using the cosine of the mid-latitude to find departure. • Use the right-angle triangle formed by DLat and departure to find the course (with arctangent) and the distance (with Pythagoras). Then compare your results to the choices given.

✅ Before You Answer

• Be sure you used the mid-latitude (average of the two latitudes) in degrees, not in minutes, before taking the cosine. • Check that your quadrant for the course makes sense: are you going south or north, east or west from the initial position? • Verify your final distance is in nautical miles and that you used DLat and departure (both in minutes) correctly in the Pythagorean formula.