Vx and Vy get a little more complicate with altitude change.
Vx increases with altitude, Vy decreases with altitude.

Robert M. Gary wrote:
BTW: There is a formula to get Vy, Vx, and Vso (and probably best
glide) for each weight. I don't have it in front of me right now. That
formula is on the Flight Engineer FAA written exam.

-Robert, CFI