I hate to admit but this young lady is ten times the sailor Zacis
 

Ronald Raygun wrote:

Yes I know about all that, but it fails to address my specific point that
the "triangle" formed by the departure and destination points and a third
point chosen in such a way that the latitude and longitude differences
make up the two sides (the third side being the great circle route) is
not actually a proper spherical triangle (and the spherical cosine rule
therefore does not apply), because the longitude difference "side" is
not a great circle.

Sorry, I misread your original post and didn't notice what triangle
you had in mind.

I've used one of them (or both) to compute the direction to point a
directional antenna to in my youth, so it's not too hard.

Easier in your youth than now, I expect! :-)

Just not any longer in memory, but nothing fancy. What I still didn't
do is to derive the sine and cosine rule from a series of rotations,
which would be a way for me to really remember the stuff. But I didn't
do that in my youth, either.

Regards,
-is
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