Hover or tap underlined Spanish terms to see their translation and exam tip.
Calcular el rumbo inicial para ir por el camino más corto desde un lugar de longitud 015º 00′ E y latitud cualquiera (excepto 90º), hasta otro de longitud 075º 00′ W y latitud 00º 00′.Calculate the initial course to sail by the shortest route from a place at longitude 015º 00′ E and any latitude (except 90º) to another at longitude 075º 00′ W and latitude 00º 00′.
Show the answer
Correct answer: c) 270º
Why it is correct
Between 015º 00′ E and 075º 00′ W the difference of longitude is ΔL = 90º W, and the arrival latitude is 0º (tan l′ = 0). In tan Ri = sin 90º / (cos l · 0 − sin l · cos 90º) = 1 / 0, the initial course is 270º for any non-polar departure latitude.
Why the others are not
- a) Departure latitude is not needed because tan l′ = 0 and cos 90º = 0 make the denominator zero.
- b) 090º would head east, taking the long way away from 075º W.
- d) Only from the poles does any meridian work; elsewhere the great circle fixes 270º.
How to work it out in the exam
- A great circle crossing the equator 90º of longitude away has its vertex at the departure point (Ri = 270º).
Where this question comes from
- Junta de Andalucía · 2020 · Convocatoria de e · CY Módulo de navegación · question 19 Official paper · Official answer key
Pending instructor review. Machine translation, not reviewed.