Well there has to be a right angle in there somewhere as the pole must be perpendicular to the ground.
Using the sine rule: sinA/a = sinB/b where a = 10, A = 90, b = 5√3, B = B Re-arrange for B, B = arcsin (b(sinA)/a) B = arcsin(5√3(sin90)/10) B = 60 degrees.
