The great circle distance from LAT 35°08.0'S, LONG 19°26.0'E to LAT 33°16.0'S, LONG 115°36.0'E is 4559 miles and the initial course is 121°T. Determine the latitude of the vertex.

Correct Answer: Option C — 45°30.9'S

The latitude of the vertex in great circle sailing is found using the formula cos(lat_v) = cos(lat1) * sin(initial_course). Given the initial course of 121°T and the departure latitude of 35°08.0'S, the calculation yields a vertex latitude of 45°30.9'S, consistent with standard spherical navigation principles found in Bowditch.