I have been thinking about this problem for awhile, but have no idea to even begin solving it. Was wondering if anyone has a clue to help me started? There's a point (x0,y0,z0) in 3D. There is a line on the X-Y plane. This line is say theta degrees (0 - 360) about the Y-axxis. If the point (x0, y0, z0) is rotated phi degrees about this line, what is the new position? This is just a problem I thought up, so I don't even know if there is enough information to solve it. Please help me, let me know what's a good step to solve it? Should I use Cartesian system, or use another one? Thanks!