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 D — 45°30.9'S

The vertex of a great circle is the point of highest latitude. Using the spherical trigonometry formula cos(Lat_v) = cos(Lat_1) * sin(Initial_Course), where Lat_1 is the starting latitude and the course is measured from the elevated pole, the calculation confirms the vertex latitude is 45°30.9'S.