[R-sig-Geo] Determining a coordinate given another coordinate, a great circle distance, and an angle

[Harry Kim]

Dear R-sig-geoers,

      I am stuck with a problem and i was hoping if you could help me.
Suppose i am given a coordinate in lat/long (say 25 lat 35 long) and a
great circle distance (say 10km). Also assume that i am given an angle
with respect to latitude (an angle from the x-axis say 30 degrees).
What would be the best way to determine a coordinate 10kms away from
25 lat 35 long with a given angle (30 degrees)?

     I think in euclidean space, I can use tangent of the given angle
and combine with the Pythagorean theorem to find the target
coordinate.

Thank you very much in advance,
Harry